（455-12.5×4）÷8.1 [29.7-（6.2+0.85）×4]÷0.3=（455-50）÷8.1[29.7-7.05×4]÷0.3=405÷8.1[29.7-28.2]÷0.3=50×1.5÷0.3=50×5=250
405÷8.1×1.5÷0.3=250
