Answer:
 -30%
Step-by-step explanation:
The percentage change in length is given by ...
 percent change = ((new length) -(original length))/(original length) × 100%
 = (51.29 -73.3)/73.3 × 100%
 = -22.01/73.3 × 100% = -0.30027 × 100%
 = -30%
The decrease in the length of the spring was 30%.