Adelaide paid $35 for a manicure and gave the manicurist a 20% tip How much money did Adelaide give her manicurist

The correct answer is:
$42.

Explanation:
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