3400000000= 2100000000=
506900000000= 4635000000=
6×7=42
66×67=4422
666×667-444222
6666×=
× = 4÷0.8= 3﹣ = 0.23=
÷ = 786﹣298= 25×0.7×4= 8.7+7=
( ﹣0.375)÷ = × ÷ × =