14e - 7f = 28
7e + f = 50
Note that if we divide the top equation through by 7, we have
2e - f = 4 add this to the second equation and we get
9e = 54 divide both sides by 9
e = 54/9 = 6
And using the second equation to find f, we have
7(6) + f = 50
42 + f = 50 subtract 42 from both sides
f = 8