You have now two polynomials one for length and one for the widht fo the rectangle.
a) The perimeter is the sum of the 4 sides, that is 2 * (length + width) = 2 * (5x^2 + 1 +x^2 + 4) = 2 * (6x^2 + 5) = 12x^2 + 10.
b) The area is length * width = (5x^2 + 1)*(x^2 + 4)
Apply distributive property to multiply:
5x^4 + 20x^2 + x^2 + 4 = 5x^4 + 21x^2 + 4
