input question: How do ensure the shelves will fit?

output answer: Use a ruler or measuring tape to mark the locations using a pencil where the rails will be installed.

input question: How to clean a child's school backpack?

output answer: After removing the contents use a mix of water and detergent to scrub all surfaces, rinse with cold water and let it dry in the sun

input question: paint

output answer:
can be used for rocks