The equation would be: V = A2^(Y/3)
The basic form of an exponential equation is y = ab^x.
The a is the starting amount. In this problem, we don't know that, so we just leave it as a.
The b is the rate. In this case, we are doubling the volume so we times it by 2.
The x is the amount of years. Since it is every 3 years, we can divide the x by 3.
