<u><em>Explanation:</em></u> The best way to find a total bill including tip (or tax if that is what you are looking for - it is found the same way), is to multiply the original total by 1 + the percentage of the tip.
Since the percentage is 20%, we add 0.20 to 1 to get 1.20. Now we multiply that by the original cost to get the final answer. 1.20*35 = 42</span>