Um I think its, To find the width, multiply the length that you have been given by 2, and subtract the result from the perimeter. You now have the total length for the remaining 2 sides. This number divided by 2 is the width.
Step-by-step explanation: You do 24÷3 because he has a string that is 24 inches long and if he wanted to divide it into 3 equal pieces . You would get 8 inches long for each piece (8x3) or (3x8)