Hello, thank you for taking the time to post your question!
The idea on this type of question is that you want to add their individual rates of work to find their combined rate, then take the reciprocal to find the total time. On this one that means taking
1 / (1/3 + 1/8) = 1 / (11/24) = 24/11 = 2.1818
Meaning that if they work together it will take about 2.18 hours to clean the house
I hope that helps you get moving in a better direction on this type of question! Feel free to reach out if you have any additional questions beyond that :)
