The next arrival of both deliveries will be in 20 days as 20 is the LCM (lowest common multiple) of 10 and 4.
Part A: As we have learned when given a pair of equations, we must always find a Point of Intersection....or, in other words...the solution of the lines given to us. As we know there can be one solution, in this case we view the graph; see where they intersect, and realize that the solution to these lines (Point of Intersection) is at (4,4).
Thus, your answer.
15:3 is the only equivalent ratio to 20:4.
