A metal block, whose dimensions in the \(x-, y\)-, and \(z\)-directions are respectively \(L \times H \times W\), is in a steady state with each of its sides all held fixed at various temperatures. If \(L\) is much smaller than both \(H\) and \(W\), show, by scaling, that the governing equation for this problem is simply the conduction term in the \(x\)-direction is equal to zero.