z varies directly as x squared. if z=16 when x=2, find z when x=5

Question

im confused about variatons!

Answer 1

z = kx²

16 = k(2)²

16 = 4k

4 = k

z = 4(5)²

z = 4(25)

z = 100

 

Answer 2

z varies directly as x squared. if z=16 when x=2, find z when x=5

z/x^2  = 16/2^2 = 16/4  = z/5^2 = z/25

z = 100