You can put this solution on YOUR website! Perimeter = sum of all the 4 sides. A rectangle has 2 equal sides of length, and
2 equal sides of width.
So the perimeter = 2*(Length + Width)
= 2*length + 2*width = 2*x + 2*width = 300 (given that length is x)
Simplifying (dividing both sides of the equation by 2)
x + width = 150
Therefore, width = 150 - x
Hope this helps :)