Question

What will the length and width be for a perimeter of 15

Answer 1

3 and 5 because 3 times 5 is 15

Answer 2

There are multiple possible answers for this.  To determine one of the possible answers you would use the formula P = 2l + 2w, where l stands for the length and w stands for the width.  I would choose a number for the length, such as a 4 and substitute it in the formula.  This would make it 15 =  8 + 2w.  Solve the equation by subtracting 8 from both sides and then dividing both sides by 2.  This would give you a width of 3.5 units.