If it is a fraction like (3a-3b)/(3a+12b)
= [3(a-b)]/[3(a+4b)]
= (a-b)/(a+4b)
A linear equation will contain a term in x has the highest degree. For example y = 2x - 5 . A non linear will contain terms with exponents 2 or higher
eg x^2 - 2x - 5 is nonlinear.
The degree is 4 because it is the largest exponent out of all the variables.