A bus is approaching a tunnel. At time t=0 seconds, the driver begins slowing down steadily from a speed of Ums-1 until, at t=15s, he enters the tunnel, travelling at 20ms-1. The driver maintains this speed while he drives though the tunnel. After emerging from the tunnel at t=40s, he accelerates steadily, reaching a speed of Ums-1 at t=70s.
A)calculate the length of the tunnel
B) Given that the total distance travelled by the bus is 1580m, find the value of U.