Question

I'm picking a number between 1-20. I add 5, then I times the number by 3. Lastly I takeaway it by 15. My answer is 42.

Answer 1

The number would be 14.

Answer 2

So (x + 5)*3 - 15 = 42
so the answer is 
42 + 15 = 15 + 3x
so solving for x:
x = 14