1/Rt=1/R1+1/R2+1/R3 where each is resistance in ohms
1) determine an expression for the total resistance Rt
2)determine an expression for the total resistance if R1=R2=R3
3)Determine an expression for the total resistance if R1=2R2=6R3

I got 1/Rt=1/R1R2R3(R2R3+R1R3+R1R2)
Rt=R1R2R3/(R2R3+R1R3+R1R2

then I got lost