2×7.8÷3.9 2.1÷(1.2-0.5)
①x-3.4=2.42
②12.8÷x=1.6
③9x-7x=3.8
④23.6-x=9.15
⑤1+0.25x=1.68
⑥0.3x+4×0.8=3.83