Acustomer wants to tip 15% on a restaurant bill that is $35.what will be th amount of tip? what is the total bill?

My parrents always make me do this in restaurants and I have found a hack for multiples of 5 % so

15%=10%+5% so find 10% then half it, then add it to 10% so
10% of something=10/100=1/10
5%+5/100=1/2 of 1/10 so find 1/10 of 35
1/10 of 35=35/10=3.5
half of 3.50=1.75
add that to 10%
3.50+1.75=5.25
tip=5.25
tip+bill=total
5.25+35.00=40.25

total bill=$40.25

Its equal to d=7.07in