Answer
given,
diameter of telescope = 2 m
time to collect area = 1 hour
Diameter of the another telescope = 6 m
The light collected by the telescope is directly proportional to the area of its primary mirror.
Area of the mirror is directly proportional to the square of diameter.
so,
6 m diameter telescope will carry (6/2)² = 9 times more light than 2 m telescope.
Time taken to collect light = 60/9 = 6.67 minutes.
now, For 12 m telescope
12 m diameter telescope will carry (12/2)² = 36 times more time than 2 m telescope.
Time taken by 12 m telescope to collect light= 60/36 = 1.7 minutes.