39-3=36

55+5=60 copies

36= 12*3

60= 12*5

Because there are three more pens and five fewer books, three good students are more than five.

Therefore, the maximum number of three good students is 12.

2.

3 liters =3000 cubic centimeters

Bottom area: 50*30= 1500 cm2.

Water height: 3000/ 1500 = 2cm.

10-2=8 cm

3.

Let the molecule be X.

2(x+ 1)=3x- 1

The solution is x=3.

So the denominator is 8.

The score is 3/8.

4.252/36=7, 12x7=84, that is, the number b is 84.