If an industry invests x thousand labor-hours, 9x19, and $y million, 1y2, in the production of N thousand units of a certain item, then N is given by the following formula.

N(x,y)=x^0.75y^0.25

What is the average number of units produced for the indicated ranges of x and y? Set up a double integral and evaluate it.

The average number of units produced for the indicated ranges of x and y is approximately ___thousand units.