Roster Form and Set Builder Form

If $A=\{x:x \mathrm{is} \mathrm{a} \mathrm{factor} \mathrm{of} 24\}$, then find $n\left(A\right)$.

If the cardinal number of the set, $A=\left\{x:3x+9\le 10, x\in \mathrm{W}\right\}$ is $n\left(A\right)=k$, then $k=$

Find the cardinal number of, $B=\left\{\mathrm{perfect} \mathrm{cube} \mathrm{numbers} \mathrm{less} \mathrm{than} 50\right\}$

If $\mathrm{A}=\{1, b, b, \{4, 2\}, \{x, y, z\}, d, \{d\left\}\right\}$  then $n\left(\mathrm{A}\right)$ is 

$\left\{\mathrm{I}, \mathrm{N}, \mathrm{D}, \mathrm{A}\right\}$ is the _____ form of the letters of the word $\mathrm{INDIA}$. (roster/set builder)

The set $\left\{x:x+8=8\right\}$ is the null set.

Write the cardinal number for, $B=$ The set of even numbers from $20$ to $40$.

If $T=\{a, l, a, h, b, d, h\}$, then $n\left(T\right)=5$.