Given ⁵∫₀ f(x) dx = 13 and ⁷∫₅ f(x) dx =6, evaluate
a) ⁷∫₀ f(x) dx
b) ⁰∫₅ f(x) dx
c) ⁵∫₅ f(x) dx
d) ⁵∫₀ 2f(x) dx