Taking the point directly under the center of the bridge as the origin, x = 20t, y = 15t, z = 10 let s be thedistance between them at time t, s^2 = (20t)^2 + (15t)^2 + 10^2 = 625t^2 + 100 2s ds/dt = 1250t ds/dt = 625t/s
when t = 3, s = √(625*9+100) = 75.6637 ds/dt = 625*3/75.6637 = 24.78 m/s
