3 seconds increases your speed from 32 to 35 miles per hour
Hence 3 seconds = 3 miles per hour(35-32 miles)
1 second = 1 mile
The function for the increase per mile is therefore:
f(x)= 1x
Where x is number of seconds travelled on the highway
The domain of a function are the possible input values for x. Since the speed limit on the highway is 65 miles, the input values for x cannot be more than 30 seconds(current speed is 35 miles per hour, 65-35=30)