A 40 kg slab rests on a frictionless floor as shown in the figure. A l0 kg block rests on the top of the slab. The static coefficient of friction between the block and slab is 0.60 while the kinetic friction is 0.40. The l0 kg block is acted upon by a horizontal force 100 N. If g = 9.8 m/s2, the resulting acceleration of the slab will be