Answer: The required number of books that Ruben had before purchases is 50.
Step-by-step explanation: Given that Ruben bought 6 new books for his collection that increased his collection by 12%.
We are to find the number of books that Ruben had before purchases.
Let x denotes the number of books that Ruben had before purchases.
Then, according to the given information, we have
Thus, the required number of books that Ruben had before purchases is 50.