Final answer:
The valid proportion to represent the problem is 40 miles / 3 hours = 120 miles / x hours. Solving for x, we find that x is equal to 9 hours.
Step-by-step explanation:
The valid proportion to represent the problem is:
40 miles / 3 hours = 120 miles / x hours
To solve for x, we can cross-multiply:
40x = 3 * 120
Dividing both sides by 40:
x = 3 * 120 / 40
x = 9 hours
Therefore, the valid proportion to represent the problem is:
40 miles / 3 hours = 120 miles / 9 hours