If you have to estimate I will put $85 and then to find 20 % you just have to kniw that 10% is equal to 8.5 you just move a decimal then you just add 8.5 plus 8.5 = 17 so 20% of 85 is equal to $17 and to find 15% you already know how much is 10%=8.5 so you just need to find 5% that is equal to 4.25 and then you just add 4.25 to 8.5 and that's equal to 12.75
