Is this a function? Explain

Yes

Step-by-step explanation:

The only reason a graph will not be a function is if it doesn't pass the vertical line test. In other words, if you draw a vertical line at any point, it will never pass through more than 1 point.

In that case, that is true, so it must be 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 !