Louis’s bill from dinner at a restaurant is $27.62 before tax. the local tax rate is 7.5%. louis would like to leave a 20% tip on the pre-tax amount. how much is the total bill?

As Louis is only leaving a 20% tip on the pretax bill, this means he's leaving 20% of $27.62
The best thing to do is to find 10% and double it.
27.62/10= 2.76 (as it rounds down)
2.76*2= 5.52
Therefore, you've got to add $5.52 to $27.62
$5.52+$27.62= $33.14
Hope this helps :)