DECA=10, decagon = 10 sides.
since each side is 1.8 long, all 10 sides will be 10*1.8 or 18 units long, so that'd be the perimeter then,
So we know that an average is the sum of the scores divided by the number of scores that were added together. In this case we are going to be dealing with 4 tests. So let's say x is the score for our fourth test. We can create this equation:

So then we need to simplify the top:

Then multiply by 4 on both sides to get rid of the denominator:

Then solve for x:

So now we know that Sam needs to score a 67 on the fourth test to have an average score of 50.
so the coat went down from 50 to 35, namely 15.
if we take 50 to be the 100%, what is 15 off of it in percentage?

70a + 55b = 905
a + b = 14
55a + 55b = 770
(70a-55a) + (55b-55b) = 905 - 770
15a = 135
a = 9
a + b = 14
9 + b = 14
b = 5