Answer: 
Step-by-step explanation:
For this exercise you need to remember:
1) The mulitplication of signs:

2) By definition, like terms contain the same variables with the same exponent.
Then knowing this, and given the equations:
and 
You must subtract the like terms, which means that you must subtract the numerical coefficients of each term.
Then, you get the result is:

Step-by-step explanation:
the area of a trapezoid is
(b1 + b2)/2 × h = (10 + 5)/2 × 4 = 15 × 2 = 30 in²
I'm assuming you mean to list the terms of the expression. Those are mn, -2n, and +8. There are 3 terms there.
Answer:
1000 is the best answer yet