Question 9
A wall with dimensions $2\times7$ squares has to be covered with ceramic tiles. There are two types of ceramic tiles that are available: the $1\times1$ (identical) tile and the $2\times1$ (identical) tile. The $2\times1$ tile can be rotated before being placed on the board. We are provided with as many tiles of each type as we need. In how many ways can we cover the $2\times7$ wall with such tiles?
