Determine the change in the internal energy of the system of blocks during the collision?

A block with a mass of m1 = 1.1 kg is pushed to the right with a force of 273 N for a distance of 8.7 m across a horizontal frictionless surface, after which the force is removed. The 1.1-kg block then collides with a second block with a mass m2 = 6.3 kg, which is initially at rest. The two blocks stick together after the collision.
I know you multiply (273N)(8.7m) to determine the work which amounts to 2375.1 but after that I am lost! please help and explain thank you!!!

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