Answer:
y = 7875
Explanation:
given y is directly proportional to x² , then the equation relating them is
y = kx² ← k is the constant of proportionality
to find k use the condition y = 35 when x = 1 , then by substitution
35 = k × 1² , that is
k = 35
y = 35x² ← equation of proportionality
when x = 15 , then
y = 35 × 15² = 35 × 225 = 7875