一4X-21=294X=29+21X=50/4X=12.5二5.9X-2.4X=10.53.5X=10.5X=10.5/3.5X=3三(X+6.3)/4=7.2X+6.3=7.2*4X=28.8-6.3X=22.5四4*2.5-4X=24X=4*2.5-24X=8X=8/4X=2