The gymnasium is 80 meters north of the playground.

(3) Because 120÷40=3 (cm),

100÷40=2.5 (cm),

80÷40=2 (cm),

Because ① the library is 45 to the east of the playground,

② The garden is 60 northwest of the playground.

③ The office building is 30 south of the playground.

So the location of the library, garden and office building is as shown in the following figure:

So the answer is: due west, playground, 80; 3、2.5、2.