\int_0^45 (60 - (B + 15))\, dB = \int_0^45 (45 - B)\, dB = \left[45B - \frac12B^2\right]_0^45 = 45 \cdot 45 - \frac12 \cdot 45^2 = 2025 - \frac20252 = \frac20252 = 1012.5 - Portal da Acústica