1 File  - 1 Pen  = 2.75
9 Files - 9 Pens = 9 x 2.75 = 24.75
If we buy 9 Pens, we have $24.75 left.
That amount can buy 14 - 9 = 5 Pens.
So 1 Pen = 24.75/5 = $4.95.
Thus 9 Files = 14 Pens = 14 x 4.95 = $69.30.
 
Check:
1 File = 69.30/9 = $7.70
1 File - 1 Pen = 7.70 - 4.95 = $2.75

9F = 14P
9F – 14P = 0 … (1)

F – P = 2.75
9F – 9P = 24.75 … (2)

(2) – (1):
5P = 24.75
P = 4.95

So 9F = 14*4.95 =   $69.30 #