C - no solution
you take the second solution and times the entire equation by -1
then simply
and you get 0x + 0y = 20
y= 1.25x+6.75
Make 31.75 y because that is the total cost he paid.
1.25x+6.75=31.75
1.25x=25
x=20
So he had 20 refills.
Using order of operations, the answer is 569.
9 and 12 have a common factor of 3 so 9/12 = 3/4
When put in matrix form, the coefficients of
... 3x -2y = 7
... x + 4y = 2
look like
![\left[\begin{array}{cc}3&-2\\1&4\end{array}\right]](https://tex.z-dn.net/?f=%20%5Cleft%5B%5Cbegin%7Barray%7D%7Bcc%7D3%26-2%5C%5C1%264%5Cend%7Barray%7D%5Cright%5D%20%20)
The determinant is 3×4 - 1×(-2) = 14.