To solve for the coefficient of variation you will need this formula:
CV = (SD/X) x 100 
Where: CV = Coefficient of Variance
 X = Mean/average
 SD = Standard Deviation
To determine which one is more variable, just get the coefficient of both and compare.
 AGE SALARY
 
 CV = (6/55) x 100 CV = (4,100/37,000) x 100
 = 10.90 = 11.08
Based on the results, salary is more variable because 10.90<11.08.