Set up two equations where x = the number.
Let x = the mystery number
x + 22 = 6 - 3x
Solve for x to find mystery number:
4x + 22 = 6
4x = -16
x = -4
The number is -4.
If you want to check your answer, you can see the sum of -4 and 22 is 18. 6 - 3(-4) also equals 18, therefore -4 is correct.