57 ÷ (1 + 25% - 3/8 - 2/5)
= 57 ÷ (5/4 - 3/8 - 2/5)
= 57 ÷ (7/8 - 2/5)
= 57 ÷ 19/40
= 120台
答:九月份计划生产机床120台.