5x+1.5=3x+9.9接下来就是5X-三x=9点9-1点五再接下来就是2x等于，八点4X=4.2
5x+1.5=3x+9.95x-3x=9.9-1.52x=8.4x=8.4÷2x=4.2
2x=8.4,x=4.2.
