Line Plots · Hard problem

A line plot shows how many laps each runner ran around the school track. Above $3$ there are $2$ X's, above $4$ there are $5$ X's, above $5$ there are $3$ X's, and above $6$ there are $2$ X's. One lap is $\dfrac{1}{4}$ mile. How many miles did all the runners run together? Write your answer as a fraction.