well, i'm just trying to get this, but I think it is
ps : w represents weeks, t represents total
(50 + 30) + (10 X w) + (15 X w) = t
example : (50 + 30) + (10 X 3) + (15 X 3) = 155
( this is considering their savings account is the same)
if you want it separate I can rewrite the answer, so please tell me below!