Answer:
After 6 days
Step-by-step explanation:
Let x represent the number of days after which the my earning and my sister's earning will be same,
∵ sister gets $ 30 per day,
So, her revenue after x days = 30x,
Also, her expenses in renting = $ 60,
Thus her earning = revenue - expenses = 30x - 60
Now, my earning is $ 20 per day,
So, my earning after x days = 20x
⇒ 30x - 60 = 20x
30x - 20x = 60,
10x = 60
⇒ x = 6
Hence, after 6 days my earning and my sister's earning is same.