The answer is:
Justin weighs 165 pounds.
Greg weighs 180 pounds.
If:
j - Justin's weight
g - Greg's weight
Then the system of equations is:
j + 15 = g ⇒ g = j + 15
1/2g = j - 75 ⇒ j = 1/2g + 75
We can replace j in the first equation:
g = 1/2g + 75 + 15
g - 1/2g = 90
1/2g = 90
⇒ g = 90 ÷ 1/2 = 180
Thus, Greg weighs 180 pounds.
Now, using the first equation, we will calculate Justin's weight:
j + 15 = g ⇒ j = g - 15
g = 180
Thus
j = g - 15 = 180 - 15 = 165
Therefore, Justin weighs 165 pounds.
