At a factory, the daily output is Q(K) = 600K^1/2 units, where K is the capital investment measured in units of $1,000. The current capital investment is $900,000. Estimate the effect that an additional capital investment of $800 will have on the daily output.

I'm not sure I am setting this up correctly.

Q'(K) = 300K^-1/2

K=900,000/1,000

Change in K=0.8

Is the problem set up by finding Q'(900) and Q'(900.8) and then subtracting the two totals?