A recent study has been carried out concerning radio propagation in railway tunnels. In this study, two railway tunnels of rectangular cross section are considered. Tunnel 1 has transverse dimensions of width a = 8 m and height b = 4 m, and tunnel 2 has the same height but a narrower width, a = 6 m. Assuming the tunnels to be empty with perfectly conducting walls, find the total number of propagation modes possible in each tunnel at 100 MHz. Which tunnel allows more modes to propagate?