30又8/25-[(20-9.744/2又2/5)*1/2-1又63/100]
=30+8/25-[(20-4.06)×(1/2)-1-63/100]
=30+8/25-(10-2.03-1-0.63)
=30+8/25-9+2.66
=21+0.32+2.66
=21+2.98
=23.98
如果本题有什么不明白可以追问,