How do i find the missing length of a rectangel

It is pretty easy to find on the internet it should pop up as the first one.

Take the measurements of the length you know, multiply it by two, take the perimeter minus the length that was multiplied by two, take that number and divide it by two, and you get your answer.

Here’s an example that might help you-

Aand b are correctly balanced reactions. they have the same number of atoms in both sides of the reaction

What is the inequality?