Based on the two different purchases, you can write equations for the price of a hotdog (h) and that of a drink (d). These equations can be solved by your favorite method to find the individual prices.
... 6h +4d = 17.00 . . . . . . Carl's purchase
... 3h +4d = 12.50 . . . . . . Susan's purchase
We can see that the difference in purchase cost (of $4.50) is due entirely to the difference in the number of hotdogs (3). Thus, the price of a hotdog must be
... $4.50/3 = $1.50
The 4 drinks are then ($12.50 -4.50) = $8, so must be $2 each. You don't need to figure the cost of a drink to determine that the appropriate answer choice is ...
... D. $1.50 for a hot dog; $2.00 for a drink.
