help needed finishing this optimization problem

[meager sky]

Did you intend for the box diagram at the bottom to be tipped onto its side? Your labeling of variables on the diagrams is off.

In order to carry out a maximization, you'll need to express everything in terms of one variable.

Make a function for the cost in terms of x and y, then use 16 = 2yx^2 to replace one variable in terms of the other.

[balmy sleet]

Did I do this right @meager sky

[meager sky]

Looks much better!