Let x represent the first number, y represent the second, and z represent the third.
x + y + z = 92
z = 3x
x = y - 7
Solve x = y - 7 for y.
x = y - 7
x + 7 = y
Fill in y and z so that we only have to worry about x for now.
x + y + z = 92
x + (x + 7) + (3x) = 92
x + x + 7 + 3x = 92
5x + 7 = 92
5x = 92 - 7
5x = 85
x = 85/5
x = 17
Solve for y.
y = x + 7
y = (17) + 7
y = 24
Solve for z.
z = 3x
z = 3(17)
z = 51
So x = 17, y = 24, and z = 51.
