The number of vacancies increases at higher temperatures. between 20 and 1020 degrees Celsius, the latttice constant of a bcc metal increase 0.5 l/o from thermal expansion. In the same temperature range the density decreases 2.0 percent. Assuming there is one vacancy per 1000 unit cells in this metal at 20 degrees Celsius, estimate how many vacancies there are per 1000 unit cells at 1020 degrees celsius?