To determine the distance at which an object should be placed in front of a convex lens to get a real image of the same size, we can use the lens formula:

1/f = 1/v - 1/u

Where:

- f is the focal length of the lens

- v is the distance of the image from the lens

- u is the distance of the object from the lens

In this case, the focal length of the lens is given as 15 cm (f = 15 cm). Since we want to obtain a real image of the same size as the object, the magnification of the image should be 1.

Therefore, the magnification formula can be used:

magnification = -v/u

Since the magnification is 1, we can rewrite the formula as:

1 = -v/u

By substituting the given focal length (f = 15 cm) and simplifying the equation, we get:

-15/u = 1

Solving for u, we find:

u = -15 cm

Now, since u represents the distance of the object from the lens, it must be positive. Therefore, the distance at which the object should be placed in front of the lens to get a real image of the