= 23.3 + (-1.8 + 6) - (18.2 - 11.7)
= 23.3 + (4.2) - (6.5)
= 23.3 + 4.2 - 6.5
= 27.5 - 6.5
= 21.0

Therefore, 23.3 + (-1.8 + 6) - (18.2 - 11.7) equals 21.0.