计算：(3/7+5/8+6/7）÷1/50
=(9/7+5/8)÷1/50
=(72/56+35/56)÷1/50
107/56÷1/50
=2675/28
0.076×1/1000×25%
=0.076×1/1000×1/4
=0.019×1/1000
=0.000019