am going to assume you meant, y is directly proportional to x2
directly proportional means is that y equals x2 times some constant value, we will call "k".
y = kx2
We are given: y = 365 when x = 15
So we can solve for k.
365 = k(15)2
365 = 225k
k = 1.62
y = 1.62x2
find y if x = 10
y = 1.62(10)2
y = 162