Maria's candy bars can be substituted by x
Therefore, Tim's total number of candies is 2x-7 (twice the amount of x, 7 less)
137 is the total number of candies sold by both, so x+2x-7 is 137.
By gathering like terms, 3x-7 must equal 137
Then, add 7 to both sides, so 3x is 144
To find x, divide both sides by 3
x=48
So, Maria sells 48 candies
Tim sells 2*48-7 candies, which is 89 candies