Finding the volume for what?
This is not a full question. If you were given the amount at the begining of 1970 (we'll call it x) and the amount at the end of 1980 (we'll call it y), we should solve them accordingly:
y-x=? (calling the answer a)
a/y=%(not answer yet, call this b)
b+100=answer
Answer:
b=(-10-a)/4
First factor out the common number:3
Then divide both sides by 3
Then simplify 30/3 to 10
Then subtract a to get your answer
