Two blocks of masses $3\ \text{kg}$ and $5\ \text{kg}$ hang from the two ends of a light string that passes over a light frictionless pulley. The pulley hangs from a spring balance fixed to the ceiling, as shown in the figure. The blocks are released and move. Taking $g = 10\ \text{m/s}^2$, the reading of the spring balance while the blocks move is

Fig. 1: A pulley hanging from a spring balance fixed to the ceiling, with blocks of 3 kg and 5 kg hanging from the two ends of the string.