X=5 y=1 this what i got when i worked it out on my paper. hope that helps.
Answer:
x = 
Step-by-step explanation:
Given
3x + k = c ( isolate the term 3x by subtracting k from both sides )
3x = c - k ( divide both sides by 3 )
x = 
Let p be the prize of a pen and m the prize of a mechanical pencils. If you buy six pens and one mechanical pencil, you spend 6p+m. We know that this equals 9, because you get 1$ change from a 10$ bill.
Similarly, if you buy four pens and two mechanical pencils, you spend 4p+2m, which is 8$, because now you get a $2 change. Put these equation together in a system:

Now, if you multiply the first equation by 2, the system becomes

Subtract the second equation from the first:

Plug this value into the first equation to get

Add 3/4 foot to 2/12 foot. The LCD here is 12.
Thus, add 9/12 foot to 2/12 foot. Answer: 11/12 foot.
Are you sure you copied down that "2/12" correctly? Note that 2/12 = 1/6