Surface area is the areas of all the faces added up. Volume is how much a 3D figure can hold.
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.
5 to the power of 2 is 25