Answer:
P.E.M.D.A.S
P: parenthesis
E: exponent
M: multiplication
D: division
A: addition
S; subtraction
the question E: Addition and subtraction
the question F: Multiplication and division
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.