Answer:
Step-by-step explanation:
Fixed monthly fee = $20
Amount charged per minute for long distance calls = $0.20
denotes total cost such that 
minutes are used for long distance calls.
Amount charged for minutes for long distance calls 
Therefore, an equation for the total cost, C, when N minutes are used for long distance calls is
-1, because the equation for the slope is y2-y1/x2-x1. So let's bring the y value in the second set of point, which is 20, and bring the first y value in the first set of points, which is 5. 20-5 is 15. Now let's subtract the x values. So the second x from the second parentheses x value is -7, and the first x value from the first parentheses is 8. -7-8 is -15. Now we have this division equation, 15/-15, which is -1. So therefore, the slope of the line will be -1.
X = amount of the 18% solution
y = amount of the 40% solution
we know the 18% solution has only 18% of alcohol, the rest is maybe water or something, now, how many liters is 18%? well, 18% of anything is just (18/100) * anything, so, 18% of x is just (18/100) *x or 0.18x, and that's how many liters are there.
likewise, how many liters are there in the 40% solution? well, (40/100) * y, or 0.4y, that many.
we know the mixture has to yield 10 liters at 20% alcohol, how many liters of only alcohol is that? well, (20/100) * 10, or 2 liters.
how much of the 40% solution? well y = 10 - x
Line c has a positive slope since it goes from -5 to -3. and kind d’s slope is 2/5 which is also positive so the answer is a)
