Question

You are serving bratwurst and hamburgers at your annual picnic. You want at least three bratwursts or hamburgers for each of your 35 guests. Bratwursts cost $1.3 each and hamburgers $1.2 each. Your budget is $150

Answer 1

If you buy 3 bratwursts for each guest that would be 1.3*3*35 = 136.5 which will fit your budget no problem.
If you buy 3 hamburgers for each guest that would be 1.2*3*35 = 126 which also fits your budget.
Whichever one you decide to buy will be no problem for that budget.

Answer 2

1.3*3=3.90
3.90*35=136.50
136.50 is all you need to provide at least three of the most expensive items.
You still have 13.50 left over