Consider f(x)=2x+1 over [1,3]. Let P be the partition consisting of points {1,3/2,2,3}. Find L(f,P), U(f,P).

I'm having trouble calculating. I have L(f,P)=17/2 and U(f,P)=23/2 but don't know how to get there.

L(f,P)=sum(inf f(x)*2)

U(f,P)=sum(sup f(x)*2)