Each bullet would cost 100/80 = $1.25 if 100 bullets cost $80.
You can approximate the square root of 30 by taking the square root of a number close to it. This is called local linearization. You can take the square root of 36, which is 6, and the square root of 25, which is 5, and state that the square root of 30 is approximately somewhere between 5 and 6
B is the first term
c is the common ratio
if the first term is x and the 2nd is y then x times c=y
so
-5 times what=10?
what=-2
c=-2
the first term is -5
-5(-2)^(n-1)
b=-5
c=-2