A block of mass 6 kg, which has an initial speed of 3 m/s at time t = 0, slides on a horizontal surface. Find the magnitude of the work that must be done on the block to bring it to rest. Answer in units of J. Also if a constant friction force of magnitude 12 N is exerted on the block by the surface, find the magnitude of the acceleration of the block. Answer in units of m/s^2.