Answer
${(a)}$ 0
${(b)}$ 9
${(c)}$ 9
Work Step by Step
${(a)}$ $${f(-1) = (-1)^{3}+1}$$
$${-1+1}$$
$${=0}$$
${(b)}$ $${f(2) = (2)^{3}+1}$$
$${8+1}$$
$${=9}$$
${(c)}$ $${f(2)-f(-1) = ((2)^{3}+1)-((-1)^{3}+1)}$$
$${=(8+1)-(-1+1)}$$
$${=9+0}$$
$${=9}$$