We were told that the shape of Charlene's mirror is a rectangle. Since the perimeter and length is given, we would find the width of the rectangle by applying the formula for determining the perimeter of a rectangle whic is expressed as
Perimeter = 2(length + width)
Thus,
90 = 2(25 + width)
Dividing both sides of the equation by 2, it becomes
90/2 = 25 + width
45 = 25 + width
width = 45 - 25
width = 20 inches