When a line is steeper than other one it means it has a greater slope. In this case the slope represents the speed of Melinda and Paul. As shown in the picture, the line that represents Paul's movement has a greater slope than the one that represents Melinda's, it means Paul ran at a faster constant speed than Melinda.
If Melinda ran at a constant velocity of 5mph and Paul ran faster than her, an equation that could represent the relationship between Paul's distance an his time has to have a greater slope than 5, which is 7.