Calculate total bill they have to pay. That is $52.35 plus the tip. Tip is 20% of $52.35 which is 20% •$52.35= 20/100•($52.35)=2/10•($52.35)=$104.7/10=$10.47.
Calculate total bill which is $52.35+$10.47=$62.82
Split the bill by four friends $62.82/4=$15.70
So they each has to pay $15.70