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

Recall that area of the triangle is 1/2*(base)*(height)1/2*(13)*(17) = 110.5the answer is 110.5