A lunar lander is descending towards the moon's surface. Until the lander reaches the surface, its height above the surface of the moon is given by y(t) = b - ct + dt , where b = 800 m is the initial height of the lander above the surface, c = 60.0 m/s, and d = 1.05 m/s . (a) what is the initial velocity of the lander, at t= 0? (b) What is the velocity of the lander just before it reaches the lunar surface