If my bill was 42.61 and leave a tip how much will they pay in all

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