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

Answer:
x + y ≤ 12
Step-by-step explanation:
Inequality:
Not more than 12 means less than or equal to 12
x + y ≤ 12
The answer is C cause if you rotate it the shape looks different but if it had rotational symmetry it could be rotated less than 360 degrees and still look the same