If you add up all of the money he made and divide it by the amount he made via tips, you will see that the percent tip he received was 16%
42.66 / 22 = 1.939, So if you are estimating than anything that is 5 or over is estimated to the top, and anything 4 or less is estimated to the bottom. So in this case 1.939 is estimated to 1.94