Write a linear (y=mx+b), quadratic (y=ax²), or exponential (y=a(b)×) function that models the data.

9x

the one below it is a function

answer:

at time x=0 we have 1000, at time x=1 we have 2000, at time x=2 we have 4000.  

so that's an initial value of 1000 and a ratio of 2,

y = 1000 (2^x)

hope this !