`c) In a pin hole camera, the distance of image from the pinhole is 20 cm, size ofobjects is 15 cm and size of object is 5 cm. Find its magnification.`
so make up your mind. You say
size of objects is 15 cm and size of object is 5 cm
which is it?
But I'd guess right off that it will involve 15/5 or 5/15