Answer:
D
Step-by-step explanation:
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:
51 grams.
Step-by-step explanation:
After 25 seconds 204 * 1/2 = 102 grams is left.
So after 50 seconds ( 2 * 25), 102 * 1/2 = 51 g are left.
Answer:
10
Step-by-step explanation:
-3x+7x-8=34+9x-2
(Combine like terms)
4x-8=32
(Add 8 to each side)
4x=40
(Divide by 4)
X=10