Explanation

Given y ∝ 1/x², we can write:

y = k/x²

Step 1: Find k

When y = 4 and x = 3:

4 = k/3²

k = 4 × 9

k = 36

Step 2: Find x when y = 9

9 = 36/x²

x² = 36/9

x² = 4

x = 2