Question

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

Answer 1

V=
`(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)

`(Vr)/(12-V)=R` or

`R= (Vr)/(12-V)`