Find the value of ∫₁² (x + f(x)) dx + ∫₂⁵ (x + f(x)) dx.

$\int_1^2 (x + f(x))dx + \int_2^5 (x + f(x))dx = \int_1^5 (x + f(x))dx = \int_1^5 x\,dx + \int_1^5 f(x)\,dx$. $= \left[\frac{x^2}{2}\right]_1^5 + 4 = \frac{25}{2} - \frac{1}{2} + 4 = 12 + 4 = 16$. Final answer: $16$