Answer:
18 + t = 42, t = 24
Explanation:
We know that Johnny travelled 18 minutes without needing the gas.
Let t represent the number of minutes he had to travel after getting gas.
Then, the total time to get to the zoo will be:
18 + t
Since it takes 42 minutes in total, the final equation will be:
18 + t = 42
t = 24