Answer:
Breadth of stamp=3 cm
Length of stamp=4 cm
Area of stamp = Area of rectangle = l*b = 3*4 = 12 cm^2
Side of square card = 12 cm
Area of card = Area of square = side^2 = 12^2 = 144 cm^2
No. of stamps that can be filled in card
= Area of card / Area of stamp
= 144/12
= 12
:. 12 stamps can be filled in a card of side 12 cm.