Answer
$a. 3$
$b. 1$
$c. 0$
$d. 2$
$e. 1$
$f. \frac{5}{2}$
Work Step by Step
$a.\quad f(g(0))=f(0-1)=2-(-1)=3$
$b.\quad g(f(3))=g(2-3)=g(-1)=-(-1)=1$
$c.\quad g(g(-1))=g(-(-1))=g(1)=1-1=0$
$d.\quad f(f(2))=f(2-2)=f(0)=2-0=2$
$e.\quad g(f(0))=g(2-0)=g(2)=2-1=1$
$f.\quad f(g(\frac{1}{2}))=f(\frac{1}{2}-1)=f(-\frac{1}{2})$
$=2-(-\frac{1}{2})=\frac{5}{2}$