f(x) = 55x + 0

Ignore the 0 because that's just to show that it
is in the form f(x) = y = mx+b, slope-intercept
form for the equation of a line.  So only look at

f(x) = 55x

You know that 

distance = rate × time

f(x) is the distance in miles, 

55 is the rate in miles per hour, 

and 

x is the time in hours.

So since distance = rate × time,

f(x) = 55x
 552 = 55x

Substitute 552 for the f(x), the number of miles.
Then solve for x, the time in hours, by
dividing both sides by 55

552/55 = x

So x =  hours 

Edwin