Question 221220
S = (a-rl) / (1-r)
.
S*(1-r) = (a-rl)
.
S-Sr = a-rl
.
S-Sr -a = -rl
.
(S-Sr-a) / -r = l
.
(-S+Sr +a)/r = l
.
(a-S+Sr)/r = l