A solid is heated by a heater that gives out heat at a steady rate. The graph in the figure shows its temperature against time. It warms from $20^\circ\text{C}$ to $80^\circ\text{C}$ in the first $2$ minutes, stays at $80^\circ\text{C}$ for the next $5$ minutes while it melts, and then the liquid warms from $80^\circ\text{C}$ to $100^\circ\text{C}$ in $1$ minute. If $c_s$ and $c_l$ are the specific heats of the solid and the liquid, and $L$ is the latent heat of fusion, then

Fig. 1: Temperature against time: rising from 20 to 80 degrees Celsius in 2 minutes, flat at 80 degrees from 2 to 7 minutes, then rising to 100 degrees at 8 minutes.