Two blocks A and B are connected to each other by a string and a spring,

Two blocks A and B are connected to each other by a string and a spring, the string passes over a frictionless pulley as shown in Block B slides over the horizontal surface of a stationary block C and the block. A slides along the vertical side of C, both with same uniform speed. The coefficient of friction between the surface of the blocks is 0.2 Force constant of the spring is 1960 `N//m` if the mass of block A is 2 kg calculate the mass of the block B and the energy stored in the spring.