For this case what we should do is write the equation of movement for each person. We have then: For Roger: r = 20 * t + 500 For Willa: r = 40 * t Equating the equations: 20 * t + 500 = 40 * t We cleared t: 40 * t - 20 * t = 500 20 * t = 500 t = 500/20 t = 25 s Answer: it did take willa 25 s to catch up Roger.