Given:
Amira = 80
Sasha = 40
Amira saves 40 per month
Sasha saves 50 per month
Let x be the number of months.
Amira = 80 + 40x
Sasha = 40 + 50x
Amira = Sasha
80 + 40x = 40 + 50x
40x - 50x = 40 - 80
-10x = -40
x = -40/-10
x = 4
Amira = 80 + 40x = 80 + 40(4) = 80 + 160 = 240
Sasha = 40 + 50x = 40 + 50(4) = 40 + 200 = 240
It would take them 4 months to have the same amount of savings.