Robin has triple as many marbles Amy. Sam has 15 more marbles than robin. Together they all have 99 marbles. How many marbles does each person have

Let: x be Amy's marbles

3x be Robin's marbles

15+3x be Sam's marbles

x+3x+15+3x=99

7x+15=99

7x=99-15 (transfer 15 to the right side of the equation, then minus)

7x/7=84/7 (divide both sides of the equation by 7)

x=12

Now substitute:

x = 12 (Amy's)

3x = 3*12 = 36 (Robin's)

15+3x = 15+3*12 = 51 (Sam's)

12+36+51 = 99

Therefore, Amy has 12 marbles, Robin has 36 marbles and Sam has 51 marbles.