Question

12R If V= ---- (r+R) Make R the subject of the equation .

Answer 1

V=$\frac{12R}{r+R}$
note, r and R are differnt
so multipl both sides by (r+R)
V(r+R)=12R
distribute
Vr+VR=12R
minus VR from both sides
Vr=12R-VR
undistribute R
Vr=R(12-V)
divide both sides by (12-V)
$\frac{Vr}{12-V}=R$ or
$R= \frac{Vr}{12-V}$