I've started seeing this type of question an awful lot. I made two equations (w is width, l is length and h is height)
√w^2+l^2 + h^2= 64 2wl + 2lh + 2wh = 14
However, I'm not sure where to go from here. How do I make use of these equations, or is there a simpler way to do the problem?
Use the identity $$(w+l+h)^2=(w^2+l^2+h^2)+(2wl+2lh+2hw)\ .$$ If you think carefully, both terms on the RHS are easily calculated from the given information. There is a small mistake in the equations you have written in your question.