Question 221220
S=(a-rl)/(1-r)


Multiply both sides by 1-r:


S(1-r) = a-rl
S-Sr=a-rl


I would add +rl to each side:
S-Sr+rl =a


Then I would subtract S and add +Sr to each side:
rl=a -S +Sr


Divide both sides by r:
l=(a-S+Sr)/r


R^2