(9-16/39×4)+(8-16/39×5)+..+(4-16/39×9)
=9+8+7+...+4-16/39×4-16/39×5-.-16/39×9
=(9+4)×6/2-16/39×(9+8+7+...+4)
=(9+4)×6/2-16/39×(9+4)×6/2
=39-16
=23
(9-16/39×4)+(8-16/39×5)+..+(4-16/39×9)
=9+8+7+...+4-16/39×4-16/39×5-.-16/39×9
=(9+4)×6/2-16/39×(9+8+7+...+4)
=(9+4)×6/2-16/39×(9+4)×6/2
=39-16
=23