Final answer:
There are 2 offices that are at least 64 square meters but less than 81 square meters.
Step-by-step explanation:
To find the number of offices that are at least 64 square meters but less than 81 square meters, we need to look at the given measurements. According to the stem-and-leaf plot, the offices in this building have the following sizes:
5: 335
6: 89
7: 1578
8: 56
From the plot, we can see that there is one office that falls within the range of 64 to 81 square meters, which is the office with the size of 78 square meters (leaf value 8 on stem 7). Therefore, the answer is a. 2 offices.