The question is incomplete.Here is the complete question.
The load that can be supported by a rectangular beam varies jointly as the width of the beam and the square of its length, and inversely as the length of the beam. A beam 13 feet long, with a width of 6 inches and a height of 4 inches can support a maximum load of 800 pounds. If a similar board has a width of 8 inches and a height of 7 inches, how long must it be to support 1300 pounds?
Answer: It must be 392 inches or approximately 33 feet.
Step-by-step explanation: According to the question, the measures (width, length and height) of a beam and the weight it supports are in a relation of <u>proportionality</u>, i.e., if divided, the result is a constant.
For the first load:
width = 6in
height = 4in
length = 13ft or 156in
weight = 800lbs
Then, constant will be:


k = 1300
For the similar beam:

L = 49.8
L = 392in or 32.8ft
A similar board will support 1300lbs if it has 392 inches or 32.8 feet long.
There is no "last term." Since the pattern is increasing by .03 each time, then the pattern continues forever.
We calculate the sum of all interior angles using this formula 180(n-2) , n=number of sides
180(40-2)= 6840
6840 ÷ 40 = 171