Nobody wants to do these because, I don't know why.
Like I said, just use the formulas
y=2x is 2,4,6,8
y=3x+1 is 4,7,10,13
y=x-5 is -4,-3,-2,-1
y=5x+6 is 11,16,21,26
Wow I just noticed these are all patterns...
Answer:
There are 5 black counters in the bag.
Step-by-step explanation:
15 green counters in the bag
The proportion of green counters is given by:

So, we have that, the total is x. So


There are 30 total counters.
How many black counters are in the bag ?
A sixth of the counters are black. So

There are 5 black counters in the bag.