A block of mass 15 kg is placed over a frictionless horizontal surface.  Another block of mass 10 kg is placed over it.  That is connected with light string passing over two pulleys fastened to the 15kg block.  A force F=80 N is applied horizontally to the free end of the string.  Coefficient of friction between two blocks is 0.6.  The portion of the string between 10 kg block and the upper pulley is horizontal as shown in the figure.  Pulley string and connecting rods are massless (Take $g=10 m{s}^{-2}$)