Afive inch bamboo shoot doubles in height every three days. if the equation y=ab to the x power, where x represents the number of doubling periods what are the values of a and b

This question was once asked before so I will put it here.

The correct answer for the question that is being presented above is this one: "x = 2; a = 5; b = 3" A 5 inch tall bamboo shoot doubles in height every 3 days. If the equation y=ab^x, where x is the number of doubling periods, represents the height of the bamboo shoot.

Well if you were to put the problem into words, it'd be:
x/-8 = -25

Thus, to solve for x, multiply both sides by -8:
x/-8(-8) = -25(-8)
x = 200