Question 828428
Let x- be the width

In finding the Perimeter, we use the formula
P=2length+2width

So,
240 = 2(99) + 2x
240 = 198 + 2x
42 = 2x
21 = x

So the width should be 21 cm, to have a length of 99 cm and a perimeter of 240 cm.

Hope that helps! :)