Question 4784
Let the number of units John sold = x
so, Harvey sold 2.5x

The difference is Harvey - John

2.5x - x = 87

1.5x = 87

divide both sides by 1.5

x = 58

John sold 58 units and Harvey sold 145 units
this makes sense because 145 is 87 units greater than 58 and also 2.5 times 58.