Let's solve it using 2 equations...just for yuks!
Let x = #passengers handled at O'Hare
Let y = #passengers handled at Hartsfield
Let 150.5 = total passengers handled at both airports
Hartsfield handled 5.5 million more than O'hare, so
Now, solve the system using substitution. Replace y in the second equation with x + 5.5 from the first equation.
Solve for x. Then use that value to solve for y in
Can you finish?