How many envelopes can be made out of a sheet of paper 3 m 24 cm by 1 m 72 cm , if each envelope requires a piece of paper of size 18 cm by 12 cm ?

Length of the sheet of paper=324cm
Breadth of sheet of paper=172cm
Area of sheet paper=lxb=324x172 cm2
Area of the piece of paper required for on envelope=18x12 cm2
Number of envelopes=$\frac{324\times 172}{18\times 12}$
                                     =258