Final answer:
To find the dimensions of the rectangle with the given perimeter of 78 cm and the relationship between length and width, a system of equations is established and solved to determine the width and length.
Step-by-step explanation:
To find the dimensions of a rectangle given its perimeter and area, with the length being a function of the width, we set up a system of equations. Let width be represented by w and length by l. The problem states that the length is three more than five times its width, so we have l = 5w + 3. The perimeter of a rectangle is given by the formula P = 2l + 2w, and we know the perimeter is 78 cm, leading to the equation 2(5w + 3) + 2w = 78. Solving this, we find the width, and substituting back, we get the length.