Answer
a) $f(2)=1$
b) $f(-1)=7$
Work Step by Step
a) $f(2)$ means output value when input value is $2$.
From the given, input value $2$ corresponds to output value $1$. So:
$$f(2)=1$$
b) $f(-1)$ means output value when input value is $-1$.
From the given, input value $-1$ corresponds to output value $7$. So:
$$f(-1)=7$$