Answer:
Let t be the cost of 1 taco and d be the cost of 1 drink. We can write the equation 2t + 4d = 11.60 for Isabella's order and 3t + d = 8.40 for Lucas's order.
To solve this system of equations, we can add the two equations together: (2t + 4d) + (3t + d) = 11.60 + 8.40
5t + 5d = 20
We can then divide both sides by 5 to find the value of t and d:
t + d = 4
Therefore, the cost of 1 taco and 1 drink is $4.
Explanation: