Answer:
x = 5.2
Step-by-step explanation:
x/(13-x) = 2/3
3x = 2(13 - x)
3x = 26 - 2x
3x + 2x = 26
5x = 26
x = 26/5
x = 5.2
A counter-example could be
There are more than 3 marbles in the bag, and the other ones are red.
Hope this helps!
Use an app on your phone just make sure you pick a gods one it will give you the answer I am not that good at math tho