Math Help - Percent change in purchasing power

1. Percent change in purchasing power

How would you calculate the percent increase or decrease in purchasing power when given the wages and index number.

Wages were $22000 four years ago, when the index was 104.$28000 today when the index is 110. The answer is 20.3%, not sure how you would calculate that.

2. $\frac{28,000 \ \div \ 1.1}{22,000 \ \div \ 1.04} \ - \ 1 \ = 0.2033$

The numerator and denominator are both re-expressing the nominal wages back to their 'base-year' purchasing-power amounts. The rational comparison of the two shows a 20.33% increase in terms of purchasing power.