Clodagh and Eva went school supply shopping together. Clodagh bought 3 packs of pencils and 5 notebooks for a total of $18. Eva bought 4 packs of pencils and 4 notebooks for a total of $16.80. How much does a pack of pencils cost? How much does a notebook cost?

each notebook costs $2.70

each pack of pencils costs $1.50

Step-by-step explanation:

system of equations:

let p = pack of pencils

let n = notebook

3p + 5n = 18

4p + 4n = 16.8

I used the elimination method by multiplying the first equation by 4 and the second equation by -3

4(3p + 5n = 18)  =  12p + 20n = 72

-3(4p + 4n = 16.8)  =  -12p -12n = -50.4

adding the new equations together you get:  8n = 21.6

n = 21.6/8

n = $2.70

solve for 'p':

3p + 5(2.7) = 18

3p + 13.5 = 18

3p = 4.5

p = $1.50

let's cover over the formula of the vertex:

y = a(x – h)^2 + k

in this formula, (h,k) are the vertex, always remember that the positive or negative value of the vertex is based on the sign it has.

for example, if the vertex is -3,-6 then both the x and y value would have the positive sign attached to it and if it were a positive x and y value, then a negative sign would be attached to it.

with that being said, for our problem the x value is a positive one so we are looking for a number with a negative sign next to it, in this case the first and second choice.

however, for the first answer choice it isn't quite part of the formula so we know that the answer choice correctly displays the x value.

to confirm, we can see if the -1 fits correctly with the second answer choice, and as mentioned above a negative number will have a positive sign attached to it. so, for our problem we can see that -1 has been changed to +1, so we can confirm that the second answer choice is correct.

hence, our final answer is y=(x - 1)^2 + 1