4÷7/3+3*3/7
=4×3/7+3×3/7
=（4+3）×3/7
=7×3/7
=3
12/13÷2/5*1/6
=（12/13*1/6）÷2/5
=2/13×5/2
=5/13
3/5÷（3/5-2/5）*3/5
=3/5÷1/5×3/5
=3×3/5
=1.8