it depends how long the width and the length is. If the length is 5 cm and the width is 4 cm the perimeter will be 18cm. All you have to do is 5 doubled because there 2 sides for the length and 4 doubled because there are 2 sides for the width. I hope I have answered your question. XD
The general formula for the lateral surface area of a regular pyramid is:

Where:
p=perimeter of a base
l=slant height
a.
a=3ft
l=4ft
p=5*a=5*3=15ft

b.
a=2.5ft
l=4ft
p=6*a=6*2.5=15ft

c.
a=1.9ft
l=4ft
p=8*a=8*1.9=15.2ft

d.
Based on a lateral surface area the blue umbrella is best choice. But, the best umbrella overall is the one with the greatest base area. General formula for regular polygon is:

For pentagon:
A=15.48ft^2
For hexagon:
A=16.24ft^2
For octagon:
A=17.43ft^2
Blue umbrella is still best choice.
Answer:
1008 in
Step-by-step explanation:
84x12=1008
84 feet times 12 inches because 12 inches is a foot.
so 84 feet times 12 inches gets your answer. 84 times 12=1008
make sense?