Answer:
310 = 120 + 10x
Explanation:
310 represents the final number she needs to by the audio system
120 represents the money she has already saved
10 represents the amount of money she will earn in x amount of hours; multiplied by x
Example, if she worked 2 hours;
310 = 120 + 10(2)
310 = 140
She would have to work more obviously to meet the $310 criteria