(1) The post office is 30 degrees west of the school, and the distance from the school is 300÷ 100=3 (cm).

(2) The library is 40 degrees north of the school, 200÷ 100=2 (cm).

Their positions are as follows:

(3) The museum is located 45 northeast of the school;

5× 100=500 (m),

It is 500 meters away from the school.

So, the answer is: East; North; 500.