It can be convenient to solve for the product xy, then see which ordered pairs will work.
... 4xy +8 = 36 . . . . . given
... 4xy = 28 . . . . . . . . subtract 8
... xy = 7 . . . . . . . . . . divide by 4
We know that (x, y) = (1, 7) and (7, 1) will work (matches d) because 1·7 = 7·1 = 7.
We know that (x, y) = (3, 2) or (4, 9) will not work (parts of a, b, c) because ...
... 3·2 = 6 ≠ 7, and 4·9 = 36 ≠ 7.
The best choice is ...
... d: (7, 1) and (1, 7)
