what is the relation between variance and coveriance

4 - (10 pts) Consider random variables X1,X2 and X3, where X1 and X3 are independent, and X2 and X3 are independent. If Var(X1)=4,Var(X2)=3,Var(X3)=2 and cov(X1,X2)=1, then calculate cov(X12X2+X3,2X1+3X3+2)