Jim bought x iphones for seven coupons each and sold y android phones for 4 coupons each. He got 20 coupons.
Julia bought the same number iphones for 3 coupons each and bought the same number Android phones for 4 coupons each. She got 20 coupons too. Please find quantity of iphones they will get and quantity of Android phones sold by Jim and got by Julia
{7x-4y=20
+
{3x+4y=20
10x=40
x=4
28-4y=20
4y=8
y=2
Answer
x=4; y=2
Jim and Julia bought 8 iphones and Jim sold 2 Android phones. Julia bought 2 Android phones.