Let \( I(x) = \int \frac{dx}{(x-11)(x+15)} \). If \( I(37) - I(24) = \frac{1}{4} \left( \frac{1}{\beta x} - \frac{1}{c x} \right) \), \( b, c \in \mathbb{N} \), then \( 3(b + c) \) is equal to