A culture in the laboratory started with 500 bacteria. Three hours later, the number of bacteria grew exponentially to 8,000. How many bacteria will there be after 4 hours?

y = 500e^(kx)

500e^(3k) = 8000
e^(3k) = 16
3k = ln16
k = 1/3 ln16
so you have
y = 500 e^(1/3 ln16 x) = 500*16^(x/3)
y(4) = 500 * 16^(4/3) = _____