You can create an equation to represent this problem. Assume that x represents the unknown number. Six times the number would be represented by 6x.
You would then increase that expression by 17 using: 6x + 17
Finally you could set this expression equal to -121 using 6x + 17 = -121
We can solve this using inverse operations:
6x + 17 = -121 (Now subtract 17 from both sides of the equation)
6x + 17 -17 = -121 - 17 (Subtract 17 from -121)
6x = -138 (Divide both sides by 6)
6x/6 = -138 / 6 (Divide -138 by 6)
x = -23
You can check with 6 * (-23) + 17 = -121
