Let's look at the formula for the rectangle's area.
l×w=300
The length is equal to 3w
3w×w=300
3w²=300
300÷3=100
100=w²
√100=10
So, the width is 10. Since the area is 300, we can divide the area by the width to find its length.
300÷10=30
So we have our length and width, now we need our perimeter.
30+30+10+10
60+20
80
The perimeter is 80 cm.
Tell me if this helps!!