You are looking for a speed in miles per hour, so start by converting 90 minutes into hours.
90/60 = 1.5
90 minutes = 1.5 hours
speed = distance/time = (105 miles)/(1.5 hours) = 70 mph
As a fraction it would be 8/5
SOLUTION
Given the question in the image, the following are the solution steps to answer the question.
STEP 1: Write the given function

STEP 2: Plot the given function
STEP 3: choose the correct graph
It can be seen from the plotted graph in step 2 that:

Hence, comparing the x-intercepts, the correct graph is seen in: