A rectangle has 4 sides. The 2 sides that are the width are equal. The two sides that are the length are equal. So, if the width is 20, we need to multiply that by 2 (because of the two sides).

20 x 2 = 40

Now we have to find the remainder of the perimeter.

146 - 40 = 106

Remember that this is between 2 sides. We need to divide this by 2 in order to get the length of 1 side.