Answer:
90 engines must be made to minimize the unit cost.
Step-by-step explanation:
Vertex of a quadratic function:
Suppose we have a quadratic function in the following format:

It's vertex is the point 
In which


Where

If a>0, the minimum value of the function will happen for 
C(x)=x²-180x+20,482
This means that 
How many engines must be made to minimize the unit cost?
x value of the vertex. So

90 engines must be made to minimize the unit cost.
Answer:
a^4 - a^3 + a^2 - 2a - (2)/(a + 1)
The answer is 43. You have to do: 180 (maximum in the triangle) - 47 - 90 (the angle that isn’t x) = 43. That’s the measure of x!
If you are saying:
(3/12) - (8/12)
Then since their denominators are the same we can subtract the numerators to get our answers.
3 - 8 = -5
Following the rule of adding and subtracting fractions, the denominators will not change unless they are different.
So: (3/12) - (8/12) = -5/12