If f(x) varies directly with x2 and f(x)=10 what is the value of f(x) when x=3

If f(x) varies directly with  

If f(x) varies directly with x then we use equation f(x) = kx

where k is the constant of proportionality

So equation becomes

We use the information and find out k

f(x)= 10

now we use the value of k and find the value of f(x) when x=3

f(x) = 10

The value of f(x) = 10 when x= 3