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
I could only answer 14. and it is 138.3
Would it be two equilateral triangles?
I'm sorry if this doesn't help I don't really know what type of triangle that is.
Answer:
To find the answer, you multiply all of them together when your finding area.. so.. 2x3x6x3 = 108