(b)
$\int_{0}^{\pi}{f(x)\sin{x\ dx +}}\int_{0}^{\pi}{f''(x)\sin{x\ dx = 5}}$
$\Rightarrow \ \lbrack f(x)( - {\cos{x)\rbrack}}_{0}^{\pi} + \int_{0}^{\pi}{f'(x)\cos{x\ dx + \int_{0}^{\pi}{f''(x)\sin{x\ dx = 5}}}}$
$\Rightarrow \ \lbrack - f(x){\cos{x\rbrack}}_{0}^{\pi} + \lbrack f^{'}(x){\sin{x\rbrack}}_{0}^{\pi} - \int_{0}^{\pi}{f''(x)\sin{x\ dx + \int_{0}^{\pi}{f''(x)\sin{x\ dx = 5}}}}$
$\Rightarrow \ f(\pi) + f(0) = 5 \Rightarrow f(0) = 5 - f(\pi) = 3\$