Answer:

I think the answer is 50 cm.

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The relationship between the object distance (denoted as "u"), the image distance (denoted as "v"), the focal length (denoted as "f"), and the magnification (denoted as "m") for a concave mirror is given by the mirror formula:

1/f = 1/v + 1/u

The magnification is defined as:

magnification (m) = -v/u

Given that the image formed by the concave mirror is twice the size of the object (m = -2), and the focal length is 20 cm, we can solve for the object distance using the magnification formula:

-2 = -v/u

v = 2u

Now, substitute the value of v into the mirror formula:

1/20 = 1/2u + 1/u

Combine the fractions on the right side:

1/20 = 3/2u

Solve for u:

u = (3/2) * 20

u = 30 cm

So, the distance of the object from the mirror is 30 cm. None of the given options (B) 50 cm, (C) 25 cm, (D) 15 cm, (A) 10 cm are correct.