12=+ 42=××
①2x<3 ②0.5y+1=8 ③81-9=72 ④x-5
4和15()[] 5和7()[] 90和30()[]
9和15()[] 13和39()[] 6和13()[]
①53+x=89
②3x+5x=12.8
③2x-6.2=2.18
④5×1.4+4x=27
⑤7x-16×4=27
⑥2.8x-1.9x=13.5