A man starts walking north at 3 ft/s from a point P. Five minutes later a woman starts walking south at 7 ft/s from a point 500 ft due east of P. At what rate are the people moving apart 15 min after the woman starts walking? (Round your answer to two decimal places.) Solution dx/dt=3 ft/s and dy/dt=7 ft/s z^2=(x+y)^2+500^2 x=3600 ft y=8400 z=v71170000 dz/dt=3600+8400/v71170000(3+7) =14.22ft/s..