The missing angle would be 35 degrees. The straight line adds up to 180 and the right angle would be 90 degrees. 180-90-55 would be 35.
You can find the circumference of the circle with the circumference equals 2pir.
circumference=2pi9
circumference=18pi
circumference=56.55 feet
you can then turn the feet into inches by multiplying by 12
(56.55 feet)x(12inches/foot)=678.58 inches
then divide 678.58 inches by 54 inches to find how many light strands are needed.
(678.58 inches)/(54 inches/strand)=12.57 strands
The common difference if there is one is the constant difference that occurs between any term and the term before it.... in this case:
There is no common difference,
dx=18,20,16,18 the difference or velocity is not constant...
d2x=2, -4,2 the acceleration is not constant...
d3x=-6,6 the thrust is not constant
Now we might be tempted to say that:
d4x=12 and say that that is constant and we COULD make a quartic equation fit all the data points, but without further data points in the sequence there is no mathematical proof that the quartic equation would produce accurate data points outside of the range given...
And solving a system of five equations for five unknowns is tedious for such a problem...a^4+bx^3+cx^2+dx+e=y
Multiply 209 by 12 to find one year which is 2508
Multiply 2508 by 4 to find 4 years which is 10032
Subtract 8500 from 10032 which is 1532
So he paid 1532 more than the cars original price
I hope thats understandable!