Answer: A bag is 4$, a drink is 7.25$.
Explanation:
Let x be the price of a bag of popcorn and y the price of a drink.
After the notation, the system of equations is as follows:
x + 3y =25.75
4x + 9y = 81.25
Multiplying the first equation by 3, we obtain:
3x + 9y = 77.25
4x + 9y = 81.25
Substracting the first ecuation from the second, we obtain the following single equation:
x = 4.00 - the price of a popcorn bag is 4$
To find y, we introduce the now found x into the first equation:
4.00 + 3y = 25.75 ⇒ 3y = 21.75 ⇒ y =7.25 - the price of a drink is 7.25$