You left out part of the problem.
I'll take a guess at what's missing.
This is Conditional Probability, requiring Bayes' Theorem.Bag M has 5 white balls and 2 red balls.
Bag N contains 3 white balls and 4 red balls.
A ball is randomly chosen from Bag M and moved to Bag N.
If a white ball is selected from Bag N, what is the probability
that a red ball was transferred from Bag M to Bag N?
. . .
We consider the two cases . . .
 White moved from Bag M: .
. . Then bag N has 4W, 4R: .
. . Then: .
 Red moved from Bad M: .
. . Then Bag N has 3W, 5R: .
. . Then: . .
Hence: . .
Substitute  and  into : .