Pretty Sure Its B I had this question Too
If n is rational, it means that

Therefore when we do n² we can write it as

Remember that the product of two integer numbers is also an integer, therefore we can guarantee that

Then we can confirm that n² is the quotient of two integers and the denominator is not zero, therefore, n² is always rational, it cannot be an irrational number
It form a right triangle
legnth of ladder is hypotonuse
bottom of ladder from wall distance is one leg
distance up wall is other leg
a^2+b^2=c^2
c=hypotonuse and a and b are legs
4^2+b^2=20^2
16+b^2=400
minus 16 both sides
b^2=384
sqrt both sides
b=8√6 ft
aprox
b=19.59ft from ground