Solution:
Denote the edge lengths by a=log2x, b=log3x, and c=log4x. The condition that the surface area numerically equals the volume is equivalent to 2(ab+ac+bc)=abc. Dividing both sides by 2abc gives a1+b1+c1=21. By the Change of Base Formula, a1=log2x, b1=log3x, and c1=log4x. Therefore log22+log33+log44=21, so log2(2⋅3⋅4)=21. From x21=24 it follows that x=242=576.
Because the surface area and volume are numerically equal,
2(log2xlog3x+log2xlog4x+log3xlog4x)=log2xlog3xlog4x.
By the Change of Base Formula with base 10,
2(log2logx⋅log3logx+log2logx⋅log4logx+log3logx⋅log4logx)=log2logx⋅log3logx⋅log4logx.
Multiplying both sides by log2⋅log3⋅log4 and simplifying gives
2(logx)2(log4+log3+log2)=(logx)3.
Using log properties and moving all terms to one side gives
(logx)2(2log(4⋅3⋅2)−logx)=0.
Thus either logx=0 or 2log(4⋅3⋅2)−logx=0. If logx=0 then x=1, but this would make each edge length of the prism 0, which is impossible. Therefore 2log(4⋅3⋅2)−logx=0. This means logx=log(242) and it follows that x=242=576.