Question

y varies directly as the square of x. When x = 5, y = 100. Find y when x = 6.

y = 105
y = 120
y = 144
y = 150

Answer 1

y varies directly as the square of x

that means
y = k x^2
where k is the "constant of variation"

you need to find k.

Answer 2

we know
When x = 5, y = 100

use those numbers in
y = k x^2