I have $225.00 in my account. I can spend al but 20% of that on some new equipment. What is the most that I can afford to spend with your company?

You can "spend all but 20%" so that means you can spend up to 80% of your money (since 20%+80% = 100%). Apply 80% to the value 225

80% of 225 = (80/100) * 225 = 0.80*225 = 180

The most you can afford to spend is $180