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,
![Retail\ Job\ Earnings = 8.50 * 20 = 170](https://img.qammunity.org/2021/formulas/mathematics/middle-school/dp1ejy60mnl96w1w9ewexiaw00hznjyuj6.png)
Her office job pays her $12 per hour and she works 15 hours per week in the office
Therefore,
![Office\ Job\ Earnings = 12 * 15 = 180](https://img.qammunity.org/2021/formulas/mathematics/middle-school/btf3g0mydxekqx2zkyogxwb7igezgbc3oq.png)
Total earnings = retail job earnings + office job earnings
![Total\ Earnings = 170 + 180 = 350](https://img.qammunity.org/2021/formulas/mathematics/middle-school/jcq2nh3sb6m8sdrv152jq1l1fbn0ggo63f.png)
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,
![Office\ Earnings = 25 * 12 = 300](https://img.qammunity.org/2021/formulas/mathematics/middle-school/k0ccfbih9lz17grx67t187uyt2qpk751xj.png)
Now increased earning is:
![Increased\ Earning = Retail\ Job\ Earning + Increased\ Office\ Earning\\\\Increased\ Earning = 170 + 300 = 470](https://img.qammunity.org/2021/formulas/mathematics/middle-school/3e0m423cfp49xf46k9390t7ddia9wx5g3d.png)
We have to find the percentage increase
The percent increase is given by formula:
![Percent\ Increase = \frac{\text{Increased earning - original earning}}{\text{original earning}} * 100](https://img.qammunity.org/2021/formulas/mathematics/middle-school/lkorh87kjuf59rsjy5ugrgsxdum1vh8vlp.png)
Substituting the values we get,
![Percent\ Increase = (470-350)/(350) * 100\\\\Percent\ Increase = (120)/(350) * 100\\\\Percent\ Increase = 0.3428 * 100 = 34.28 \approx 34.3](https://img.qammunity.org/2021/formulas/mathematics/middle-school/f0rch13a8q693ouh81kzpazsh9a498gazp.png)
Thus her percentage increase in total weekly pay is 34.3 %