You can spot a linear equation when the highest degree for a variable in the equation is 1.
E.g.
y = 2x +4
The highest power of x in this equation is 1, since variable x of the 2x is x is to the power of 1, and 4 is a constant where you can imagine it to have an x but to the power of 0.
E.g.
y=x^2 + 2x +4
In this case, this would be an quadratic equation because the highest power that the variable x has in this equation is 2 (x to the power of 2).
