Rates Questions' Explanations

Hi, 

In pre-algebra section there are rates courses and after those there is a quiz, obviously. But in that quiz, there are some questions that contain 3 different parameters like 6 people, 4 wall, how many minutes it takes people to paint them. 

The problem is there is no course on these kinds of questions.

Could you add a video about how to solve these rates questions?

Thanks