Each of Exercises 61 through 68 involves either the chain rule for partial derivatives or the incremental approximation formula for functions of two variables.

The output at a certain plant is Q(x, y) = 0.08x² + 0.12xy + 0.03y² units per day, where x is the number of hours of skilled labor used and y is the number of hours of unskilled labor used. Currently, 80 hours of skilled labor and 200 hours of unskilled labor are used each day. Use calculus to estimate the change in output that will result if an additional 1/2 hour of skilled labor is used each day, along with an additional 2 hours of unskilled labor.