Leo had twice as many stickers as John at first. Leo gave away three times as many stickers as John. John was left with 10 fewer than the number of stickers he gave away. Leo had 15 stickers in the end. How many stickers did John have at first?
L=2J Leo had twice as many as John
let j = how many J gave away
L-3j = 15 Leo gave away 3 times as many as John gave away and had 15 left
substitute 2J or L
2J -3j =15
J-j = j-10 after he gave j away, John had 10 less than he gave away
2J-4j =-20 subtract from the last equation ending in =15 to eliminate J