Evaluate the integrals for $f(x)$ shown in the figure below. The two parts of the graph are semicircles.

a) $\int_0^2 2 f(x) \,dx =$

b) $\int_0^6 4 f(x) \,dx =$

c) $\int_1^4 2 f(x) \,dx =$

d) $\int_1^6 \mid 5 f(x) \mid \,dx =$