Question

I dont understand how to solve for a variable when there are two of the same variable, how do i solve for R1?

Answer 1

$\bf R_1R_2=RR2+RR_1\implies R_1R_2-RR_1=RR2 \\\\\\ \stackrel{\textit{common factor}}{R_1(R_2-R)=RR_2}\implies R_1=\cfrac{RR_2}{R_2-R}$