Sophia and tyler are running around a 400-meter track. they start running from the same place, at the same time. sophia runs at a speed of 5 m/s and tyler runs at a speed of 4 m/s. how long will it take sophia to lap tyler?

To answer this item, we let x be the time in which Tyler and Sophia will be able to cover the same distance along the circular track. Since Sophia runs faster, she will be able to finish the track and y meters more while Tyler will be able to finish y meters only. 
                                             5(x)  = 400 + y
                                             4(x) = y
The values of x and y are 400 and 1600. Thus, it will take 400 seconds for then to meet again.