That's simplied already, unless they want a decimal then it's .6 or something
X equals 60 degrees (80-20=60)
So we can start with the full of possibilities and eliminate them one by one.
The full set is {0,1,2,3,4,5,6,7,8,9}.
Now we know that any prime greater than 2 is odd as otherwise it would have 2 as a factor, so we can eliminate all of these digits that would be an even number, leaving:
{1,3,5,7,9}
We also know that any prime greater than 5 cannot be a multiple of 5 and that all numbers with 5 in the digits are a multiple of 5, so we can eliminate 5.
{1,3,7,9}
We know that 11,13,17 and 19 are all primes, so we cannot eliminate any more of these, leaving the set:
{1,3,7,9} as our answer.
ANSWER:
The surface area of the star is 3.2700 x 
square kilometres.
EXPLANATIONS:
Diameter of the star = 1.8083 x 
Km.
Surface area of the star = 4
Where n is the radius of the star.
So that;
n = 
= 0.90415 x
n = 0.90415 x Km
Thus,
Surface area = 4 x 
= 326994889
Surface area = 3.2700 x 
Therefore, the surface area of the star is 3.2700 x square kilometres.
