he saved 1/4 (25%) of what he needs to buy the shoes. 25 x 4 =100 =full price
21 x 4 =84. and also if you can do 84 - 25% on a calculator, the 25% would turn to 21, or at least in mine it did. Total price of shoes - money saved = money needed to buy shoes, which is $63.
Since 12 cost $27, you can use compatible numbers to make it ~$28. So, then for 6, it would cost $14 because you just halve everything. Is that what you are getting at?
