Firstly, they pay $7 as an entrance fee.
Then, they bought 5 hot dogs for an unspecified amount, x. The amount of hot dogs times x would equal the total price of the hot dogs.
Same principle for the popcorn and pretzels.
The expression would be 7 + 5x + 4y + 2z.
Now that we know the prices, we can plug them into the expression.
7 + 5 (4) + 4 (3) 2 (2)
7 + 20 + 12 +4 = 43
43
Hope this helps!