If you let the convenience fee equal x, then...
(2×17.25)+(2×1)+(2×x)= 40.50
There are 2 girls so we multiply all the charges by 2. Add them together and you'll get 40.50. Now if we solve for x, we will get the amount of the convenience fee.
2×17.25 + 2×1 + 2x = 40.50
34.50 + 2 + 2x = 40.50
36.50 + 2x = 40.50
2x = 40.50 - 36.50
2x = 4
x = 2
Each girl paid a 2 dollar convenience fee.

The answer is the third option, -7.
Hope this helps.
200,000 because the numbers in the middle are low
To solve this, we just need to plug in the numbers.
4^2-4*3/2
Now solve!
4^2-4*3/2
16-4*9
16-36
-20
There's your answer!
Any questions?
Let A be the event 'made by Apex and defective':
P(A) = 0.67 x 0.11 = 0.0737
Let B be the event 'made by B-ink and defective':
P(B) = 0.33 x 0.06 = 0.0198
Let C be the event 'made by Apex or B-ink and defective':
P(C) = P(A) + P(B) = 0.0737 + 0.0198 = 0.0935
P(defective and made by Apex) = 0.0737/0.0935 = 0.788
The answer is 0.788 or 78.8%.