57乘1.38+13.8乘4.3
=1.38x(57+43)
=1.38x100
=138
五分之三乘4.2-1.2除三分之五
=五分之三乘4.2-1.2乘五分之三
=3/5x(4.2-1.2)
=3/5x3
=9/5
=1.8