y = 17, and x - y = 5. Let's solve second equation for x: x = 5 + y Substitute that into first equation: 5 + y + y = 17, 2y = 12, y = 6 Then, substitute y into second equation: x - 6 = 5 x = 11 Calculated numbers are: 6 and 11. 11 and 6. you can do this quite quickly by trial and error. For similar problems using higher numbers use simultaneous equations as above.