If you add the two purchases, you find 9 hotdogs and 9 hamburgers cost 24.75. One hotdog and one hamburger will cost 1/9 of that total, or 2.75.
... One hotdog and one hamburger costs $2.75.
_____
This is what your question asks. Usually, we want to know the individual costs of the items. If we multiply this total by 5, then we have the cost of 5 hotdogs and 5 hamburgers: 13.75. This $1.75 more than the cost of 5 hotdogs and 4 hamburgers, so the cost of a hamburger must be $1.75
... One hotdog costs $1.00
... One hamburger costs $1.75
