Answer: a) 2092278989 b) 576, c) 
Step-by-step explanation:
Since we have given that
Number of students = 16
Number of desks = 16
a) How many days must pass before the class must repeat a seating arrangement?

If the number of rows = 4
b) How many seating arrangements are there that put Larry, Moe, Curly, and Shemp in the front seats?

c) How many seating arrangements are there that put Larry, Moe, Curly, and Shemp in the front seats?

Hence, a) 2092278989 b) 576, c) 
20: 30-4 x (2+5)=2
21. 17-(8-5)= 14
22. You put (10/2)-3+1, but it isn't necessary
Explanation: to solve these equations, use PEMDAS (parentheses, exponents, multiplication, division.) these equations don't involve exponents, though, so ignore that part. If 30 is left alone, you would multiply 4x2 before doing anything else. This would mean you would have 30-8+5' which gets you to 27, an incorrect answer. However, if you put parentheses around (2+5), you add those first, meaning you would then have 30-4(2+5) = 30-4(7) = 30-28= 2.
Try to do the rest; if you're still having trouble add a comment
The midpoint would be (7, 5)
The midpoint of any two points is simply the average of the x points and the average of the y points. So we'll start by averaging the 2 x points together. To take an average, we add the two numbers together and divide by 2.
X VALUE
4 + 10 = 14
14/2 = 7
Now do the same for y
Y VALUE
22 + -12 = 10
10/2 = 5
Using those answers we can create the ordered pair (7, 5)
2x^2 - y when x + 3 and y = -2
2(3)^2 - (-2)
2(9) + 4
18 + 4
22
Hope this helps,
Brian