Andrew gave you the answer, here is some background information that may help understanding;

From Wikipedia;

"In mathematics, a polynomial is an expression of finite length constructed from variables (also called indeterminates) and constants, using only the operations of addition, subtraction, multiplication, and non-negative integer exponents. However the division by a constant is allowed, because the multiplicative inverse of a non zero constant is also a constant. For example, x2 − x/4 + 7 is a polynomial, but x2 − 4/x + 7x3/2 is not, because its second term involves division by the variable x (4/x), and also because its third term contains an exponent that is not an integer (3/2)."

In Andrews answer, "a" and "b" are both to the power of +1. As they are to the power of a positive integer, the answer perimeter=22a+22b qualifies as a polynomial

P= 2*Length + 2*width

2(4a+3b) + 2(7a-2b)

8a+6b +14a-4b

22a+2b