Question

Answer 1

\(a,0-\left(-13\right)=0+13\\ b,\left(-6\right)-0=-6\\ c,\left(-7\right)-\left(-7\right)=-7+7=0\\ d,13-\left(-21\right)=13+21=34\)

Answer 2

\(0-\left(-13\right)=0+13=13\)

\(\left(-6\right)-0=-\left(6+0\right)=-6\)

\(\left(-7\right)-\left(-7\right)=\left(-7\right)+7=0\)

\(13-\left(-21\right)=13+21=34\)