Suppose there is a room for three people in the first arrangement and a room for five people in the second arrangement. According to the same number of people in the two arrangements, the following formula can be obtained.

5×4+3×A+5=2×4+5×B

Simplify, own

17+3×A=5×B

B=( 17+3×A) /5

The number of rooms is certain, so

5+A=2+B

5+A=2+( 17+3×A) /5

A= 1，b=4

So the number of people =5×4+3× 1+5=2×4+5×4=28 (people).

Number of rooms =5+ 1=2+4=6 (rooms)

Hehe, I haven't done a primary school topic for nearly ten years.