It is given in the problem that in 1975, the number of restaurants chain is 15,250.
It is also given in the problem that 2000, the total number of restaurants is 21, 655. Therefore, the solution is is shown below:
% increase= ((# of restaurants is year 2000 - # of restaurants in year 1975)/number of restaurants in year 2000) * 100
% increase = (21,655-15250)/21,655 *100
% increase = 29.58%
Answer is 29.58%