First, let's simplify each of the fractions separately.

5b / (b - 3) = 5

(b + 6) / (2b - 6) = (b + 6) / 2(b - 3) = (b + 6) / 2(b - 3)

90 / (b^2 + 66)

Now, let's multiply all the fractions together:

(5) ((b + 6) / 2(b - 3)) (90 / (b^2 + 66))

= (5(b + 6) * 90) / (2(b - 3)(b^2 + 66))

= (450(b + 6)) / (2(b - 3)(b^2 + 66))

= (450b + 2700) / (2b^3 - 6b^2 + 66b - 198)

So, the simplified expression is (450b + 2700) / (2b^3 - 6b^2 + 66b - 198).