Answer:
the firm's average salary increased by 40%
Explanation:
the average salary for last year = [(5 x $25,000) + (2 x $60,000) + $255,000] / 6 = $500,000 / 6 = $83,333.33
this year's average salary = [(5 x $25,000) + (2 x $60,000) + $455,000] / 6 = $700,000 / 6 = $116,666.67
this means that the average salary has increased by = [($116,666.67 - $83,333.33) / $83,333.33] x 100 = 40%