j = g - 15 ---- Justin weighs 15 lbs less then Greg
1/2g = j - 75 --- half of gregs weight is 75 lbs less then justins
so we sub g - 15 in for j in the 2nd equation
1/2g = j - 75
1/2g = g - 15 - 75
1/2g - g = - 90
1/2g - 2/2g = -90
-1/2g = -90
g = -90 * -2
g = 180
j = g - 15
j = 180 - 15
j = 165
so justin (j) weighs 165 lbs and greg (g) weighs 180 lbs
