A middle school bought 30 pens and 45 brushes for * * * in recognition of outstanding students in the calligraphy competition.

(1) Let the unit price of pen be X yuan, then the unit price of brush is X+4 yuan.

30X+45(X+4)= 1755

30X+45X+ 180 = 1755

75X= 1575

X=2 1

X+4=2 1+4=25

2①: If you buy X pens, then the number of brushes is105-X.

2 1X+25( 105-X)=2447

2 1X+2625-25X=2447

4X= 178

X=44.5

It is impossible to buy 0.5 pieces, so Mr. Wang said that it was wrong for him to use this money to buy only these two pieces.

② According to the calculation in ①, in order to make the number of purchases an integer, 2 yuan or 6 yuan (an integer less than 10) must be subtracted from the total payment.

If you subtract 2,

2 1X+25( 105-X)=2445

2 1X+2625-25X=2445

4X= 180

X=45

If the number of pens purchased is 45, the number of brushes purchased is 60,21x45+25x60 = 2445 yuan.

If you subtract 6,

2 1X+25( 105-X)= 244 1

2 1X+2625-25X=244 1

4X= 184

X=46

If the number of pens purchased is 46, then the number of brushes purchased is 59,21x46+25x59 = 2441yuan.

So the unit price of the pen may be 2 yuan or 6 yuan.