The volume is in the first case, xyz in the second.
In the first case, x= 1.070- 4y so . Differentiating that, which gives either y= 0 or y= 2.140/12= .1783. y= 0 gives a package of volume 0- obviously the maximum. So y= .1783 and then x= 1.070- 4(.1783)= 1.070- 0.7132= 0.3568. That makes the maximum volume
I don't think there is enough data to do the other case so I hope this was what you meant! Are you mailing a package?