Answer:
He can fit 2 more DVD's on the shelf.
And he'll have about 12 mm of extra space left.
Explanation:
40×1.4 = 56cm This is the length of space the 40 DVD's will take up.
60-56 = 4cm This is the amount of space left.
4/1.4 = 2.857 the number of DVD's that will fit.
Of course, the decimal represents a partial DVD which is worthless.
Just to be sure, 2×1.4 = 2.8cm OK. But 3×1.4= 4.2cm which is 2mm too much