Whats the problem? just substitute. For example: 3x-5 if x=4 so what you do is this; 3(4)-5=7
Every linear graph is just a straight line, so if there are any curves or unnatural shapes, than you know it is not linear. As for equations, if it can be shaped into y=mx+b where m and b are numbers, then it will be a linear equation.
You know you are finished dividing when you can no longer simply & when you plug it back in to check the answer
A home mortgage is usually D.20-30 years
Zoom factor will be the number to prove they’re the same