A 4 kg block rests on a rough horizontal table. A light inextensible string tied to it runs horizontally to a light frictionless pulley at the table's edge and then hangs vertically, carrying a 2 kg block. The coefficient of kinetic friction between the 4 kg block and the table is 0.25. The system is released and the blocks slide. Take g = 10 m s⁻². What is the tension in the string?