80÷x=20 12x+8x-12=28(2x-1)+10=37 1.6x+3.4x-x-5=27(3x+5)÷2=(5x-9)÷3 x-21×=4 x÷=÷
1-+-+-
1375+450÷18×25
55×(++++)
++++++++
2.009×43+20.09×2.9+200.9×0.28