Maths questions

One day , the initial temperature of a city in the morning is 23.5℃. The temperature rises 8.49℃ at noon. It then drops 5.32℃ in the afternoon. It drops a further 6.86℃ at
night.

(a)Use a directed number to represent the total temperature difference of the city between the morning and the night time on that day
the morning and the night time on that day.

23.5-(23.5+8.49-5.32-6.86)
=3.69dc

(b)Find the temperature of the city at night on that day.

23.5+8.49-5.32-6.86
=19.81dc

2007-09-26 19:38:56 補充：
答錯少少......23.5-(23.5 8.49-5.32-6.86)= 3.69dc

2007-09-26 19:39:08 補充：
23.5-(23.5 8.49-5.32-6.86)=( )3.69dc

2007-09-26 19:39:14 補充：
23.5-(23.5 8.49-5.32-6.86)=(加)3.69dc