In this question the graph is missing but we have sufficient information to find the time Johonson's family will tae to travel the given distance.
The concept we are going to use is the relation between the speed distance and time to find the time .
Formula is given by

This can also be rearranged to

Now we can use this formula to find the time for Johonson's family
It is given that the Speed = 60 miles per hour
And also Distance = 420 miles
Using the formula above we get

So
Time = 7 hours