12x-2 I think that’s right I’m not really sure
The rate a computer works is 1/time. Working together, you add the rates.
Let new computer be x, old computer be y.
x = y - 7

Rounded to nearest tenth gives:
x = 23 hours
15% = 0.15
tip = 15 * 0.15 = 2.25
5% = 0.05
tax = 15 * 0.15 = 0.75
total = 15 + 0.75 + 2.25 = $18
3x2 is six. If you do that across, you would get 6/6 for both. 6/6 - 6/6 is how much?