Z1+z2=(1+i√7)+(3-i√7)=1+3+i√7-i√7=4
z1-z2=(1+i√7)-(3-i√7)=1-3+i√7+i√7= -1+2i√7
z1*z2=(1+i√7)*(3-i√7)=3-i√7+3i√7-7i²=3+7+2i√7=10+2i√7
z1/z2=(1+i√7)/(3-i√7)=( (1+i√7)*(3+i√7) )/( (3-i√7)*(3+i√7) )=(3+4i√7+7i²)/(9-7i²)=(3-7+4i√7)/(9+7)= (-4+4i√7)/16= -1/4+(i√7)/4