The missing side length would be 8
Answer:
12.5
Step-by-step explanation:
A 10x10 grid would have 100 units. If you divide it into 8 equal units you would do:
100 / 8
Which gets you, 12.5

You pass the free terms wich don't contain 'x' in the othe part of the equal with changed signe ans the same for the terms wich contain x.
I have two methods for you