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