26) A

‘a’ is inversely proportional to ‘b²’.
a ∝ 1/b²

In order to turn this inequality into an equation, we need to use a constant (let us say ‘k’)

a ∝ 1/b²
a = k/b²

When a = 9, b = 4
a = k/b²
9 = k/4²
k = 9 x 4² = 9 x 16 = 144

When a = 4, b = ?
a = k/b²
b² = k/a
b² = 144/4
b² = 36
b = 6