Expression with Variables

Please read the following paragraph and answer the question at the end:
We learnt in arithmetic that we can find value of expressions like (2 x 10) + 5, 3 x 100 + 2 x 15  using BODMAS. These expressions are formed by using numbers like 2, 3, 4 and  so on. To form expressions we use all 4 operations like addition, subtraction, multiplication and division. For example, to form (2 x 10) + 5, we have multiplied 2 by 10 and then added 5 to the product. These are all arithmetic or number expressions.
Expressions can be formed using variables too. Like  x + 10 or 2x + 6 or y-100 etc. These expressions using variables are obtained  by operations of addition, subtraction, multiplication and division on variables. For example, the expression x + 10 is obtained by adding 10 to variable x.
We also know that variables can take different values; they have no fixed value. But they are numbers. That is why as in the case of numbers, operations of addition, subtraction, multiplication and division can be used in case of variables as well.
Please also note that while a number expression like 2 x 3 + 6 can be immediately evaluated, expression with variable like 2x + 5 can not be evaluated until the value of the variable is known. 
Based on above paragraph, select the correct statement?

Please read the following paragraph and answer the question at the end:
We learnt in arithmetic, that we can find value of expressions like (2 x 10) + 5, 3 x 100 + 2 x 15  using BODMAS. These expressions are formed by using numbers like 2, 3, 4 and  so on. To form expressions, we use all 4 operations like addition, subtraction, multiplication and division. For example, to form (2 x 10) + 5, we have multiplied 2 by 10 and then added 5 to the product. These are all arithmetic or number expressions.
Expressions can be formed using variables too. Like  x + 10 or 2x + 6 or y-100 etc. These expressions using variables are obtained  by operations of addition, subtraction, multiplication and division on variables. For example, the expression x + 10 is obtained by adding 10 to variable x.
Identify which one of the following is an expression with variable?

If $a=2, b=3$ and $c=4$ then the value of $a^3+b^3+c^3+3abc$ is _____ .

Omar helps his mother $1 \mathrm{hour}$ more than his sister does. If Omar helps his mother for $A \mathrm{hours}$ then write the value of $A$. (Take the variable as $x$)

Write the expression: Area of the rectangle with length $k$ units and breadth $n$ units is $P$ square units then find $P.$

Choose a letter $x, y, z, p$ etc...., wherever necessary, for the unknown (variable) and write the corresponding expressions:

Write algebraic expressions for $10$ divided by $q$ in $\frac{p}{q}$ form.