Step-by-step explanation:
Asuming object is a rectangle. We know that to find the perimeter of a rectangle we must add all the sides.
Therefore the formula wound be "b + b + l + l". To simplify this equation we can goup the similar sides as "2b + 2l".
Since we know the perimeter of the rectangle lets equate this simplified formula to 400:
2b + 2l = 400
Now because we know the breath lets replace it with the b position in tge formula.
2(50) + 2l = 400
Now lets use simple algebra to solve.
100 + 2l = 400
2l = 400 - 100
2l = 300
l = 150
Therefore, the lenght is 150cm
