25. Books were arranged in shelves. There were 12 books in each sheit except for 3 shelves which were emply. John reananged the books so that all the shelves had 10 books each. How many shelves had books at first?

Let's denote the number of shelves that had books at first as \( x \). Given that there were 12 books in each shelf except for 3 empty shelves, the total number of books at first can be represented as: \[ 12(x-3) \] After John rearranged the books so that all the shelves had 10 books each, the total number of books remained the same. Therefore, we can set up the equation: \[ 12(x-3) = 10x \] Now, we can solve this equation to find the value of \( x \), which represents the number of shelves that had books at first. Solve the equation by following steps: - step0: Solve for \(x\): \(12\left(x-3\right)=10x\) - step1: Expand the expression: \(12x-36=10x\) - step2: Move the variable to the left side: \(12x-36-10x=0\) - step3: Subtract the terms: \(2x-36=0\) - step4: Move the constant to the right side: \(2x=0+36\) - step5: Remove 0: \(2x=36\) - step6: Divide both sides: \(\frac{2x}{2}=\frac{36}{2}\) - step7: Divide the numbers: \(x=18\)