Answer: 5%
Explanation:
First notice that she contributes $300 a month and annually means yearly, so find the amount that she contributes yearly by multiplying 300 by 12 because there are 12 months in a year. 
 
300 * 12 = 3600 
Now to find the percentage, divide the amount she contributes in year by her annual salary. 
3600/ 72000 = 0.05 
Convert 0.05 into a percent by multiplying 0.05 by one hundred. 
0.05 * 100 = 5%