The percentage increase in total weekly pay is 34.3 %
Solution:
Retail job pays her $8.50 per hour and she works 20 hours per week in that job
Therefore,

Her office job pays her $12 per hour and she works 15 hours per week in the office
Therefore,

Total earnings = retail job earnings + office job earnings

Thus original earnings is $ 350
She starts working an extra 10 hours a week at her office job
She already worked 15 hours per week in office job, now it becomes,
15 + 10 = 25 hours per week
Her office job pays her $12 per hour. Therefore,

Now increased earning is:

We have to find the percentage increase
The percent increase is given by formula:

Substituting the values we get,

Thus her percentage increase in total weekly pay is 34.3 %