X+2/5X=21 (5x+2x)/5=21 7x/5=21 x=15 x-0.25x=3 0.75x=3 3/4x=3 x=4 4/5x-2/5x=1/2 2/5x=1/2 x=5/4 3.6x除以2=2.16 3.6x=4.32 x=1.2
