3又3/5 + (6/25)÷(3/5)×10 - 9/10
=18/5 + (6/25)×(5/3)×10 - 9/10
=18/5 + (2/5)×10 - 9/10
=36/10 + 4 - 9/10
=27/10 + 4
=6.7