I need help with c would really be thankful if you give me detail how it is solve

Exercise 2. Use Z and Z1 transform to compute the convolution a. x1(n)={1,2,3,4,5} and x2(n)={1,1,1} b. x1(n)=(51)nu(n) and x2(n)=2nu(n) c. x1(n)=nu(n) and x2(n)=2nu(n1)