A t shirt was on sale. 20% off now £36 what was the original price

Two ways to do this:
1) find 20% of £36 and subtract that from £36
20% = 0.20 (divide % by 100)
36 x 0.20 = 7.20
36 - 7.20 = £28.80

2) understand that a shirt that is 20% off now costs 80% of the starting price. Directly calculate that number.
80% = 0.8
36 x 0.8 = £28.80

Let me know if you have questions. Have a good evening!