so the growth factor is the base of the exponential term, so the base of y = 34 * 4^x is 4.
the initial amount is the amount at x = 0
y = 15 * 3^xy = 15 * 3^0y = 15 * 1y = 15 is the initial amount
the decay factor of y=17×0.2^x is same as the growth factor, it is 0.2
