Answer :
assuming you want to tip 20% because you had a very nice waiter...
42.61(0.20)=8.52
42.61+8.52=$51.13
if they're good but not that good 15% is
42.61(0.15)=6.39
42.61+6.39=$40
42.61(0.20)=8.52
42.61+8.52=$51.13
if they're good but not that good 15% is
42.61(0.15)=6.39
42.61+6.39=$40