What's the answer to find y when x=9 if y varies directly as the square of x, and y = 100 when x = 5

"y varies directly with square of x"

y = kx²

where "k" is the constant of variation you need to solve for first.

when y = 100; x = 5

100 = k (5) ²

100 = 25k

100/25 = k

4 = k

Now you can solve for y when x = 9

y = 4 (9) ²

y = 4 (81)

y = 324