A human heart beats at an average of $80$ beats per minute, the number of times it beats in an hour is written in scientific notation as $k \times {10}^3$

Write the value of $k$.

A human heart beats at an average of $80$ beats per minute, the number of times it beats in a day is written in scientific notation as $k \times {10}^5$.

Write the value of $k$.

A human heart beats at an average of $80$ beats per minute, the number of times it beats in a year is written in scientific notation as $4.2048\times {10}^k$.

Write the value of $k$.

A human heart beats at an average of $80$ beats per minute, the number of times it beats in $100$ years is written in scientific notation as $k\times {10}^9$.

Write the value of $k$.

Give an example and verify the following statement.

The collection of all non-zero rational numbers is closed under division.

Give an example and verify the following statement.

Subtraction is not commutative for rational numbers.

Give an example and verify the following statement.

Division is not associative for rational numbers.

Give an example and verify each of the following statements.

Distributive property of multiplication over subtraction is true for rational numbers. That is, $a(b-c)=ab-ac$.