1/15 + 5/?=9/10
1/15 + 5/?=9/10 subtract 1/15 from both sides
5/? = 9/10 - 1/15 get a common denominator on the right (30)
5/? = 27/30 - 2/30
5/? = 25/30
5/? = 5/6 so ? = 6
1/15 +5/x=9/10
(x +75)/15x=9/10
10x +750=135x
125x=750
x=6
