Would like the best way to explain two variable equations to 9th grader.

Answer 1

This forum isn't ideally suited for long explanations. A simple web search for word problems in two variables will give lots of examples and explanations. For starters, you might try

http://www.purplemath.com/modules/systprob.htm

Answer 2

a rectangle has a perimeter of 26 cm and one of its sides has a length of 5cm sketch the rectangle and label all of its side lengths