The stem-and-leaf plot lists the ages of customers in a bookstore. How many customers are 19 or younger?

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Step-by-step explanation:

1. The answer would be (D). This is because you will plug is the (x) of the ordered pair into the equation(y=-2x), so first off would be (y=-2(-2)). since your multiplying a negative time a negative, you will get your (y) which is 4. Now you do this with the rest. -2(1)=-2 and -2(3)=-6.
2. This would be (A). This answer is simple. First you will take one of the equations (y=-x-1) and plug x into it's place so, y=-3-1, getting your answer(y) as being -4. Now you do the same with the other pair. y=-5-1, getting -6, showing (A) as your answer.
3.The answer will be (A)y is 2 times x. this is because you wou would make out the equation from the answer (y=2x). Now knowing your equation, all thats left is plugging in your (x) factors. so y=2(1), getting your (y) value of 2 and you would do this with the rest of your x factors. 
4. y=5+x
    y=5+(2)= 7
    y=5+(3)= 8
    y=5+(4)= 9
5. (B)y is 3 times x
    y=3(x)
    y=3(3)=9
    y=3(4)=12
    y=3(5)=15
6. (C)y is 6 less than x
    y=6-(x)
    y=6-(8)=2
    y=6-(9)=3
    y=6-(10)=4