Each angle is 180(p-2)/p.
180-{360}/{p} = k
So 360/p has to be an integer.
360 = 2^3 * 3^2 * 5^1
So there are 4 * 3 * 2 = 24 possibilities, but we exclude 1 and 2, because p > = 3
So , 24 -2 = 22
Hence, choice (c) is the right answer

@pratik0809 It is asked to create subset so that NO two elements sum to 11. So Null set satisfies right ?
Logic here is, for a usual case (without any conditions), we can have 2^n subsets for a set of n elements. Why ? because each element can either be present or not in the subset. So each element can have two options giving a total of 2^n possibilities.
Here, we have 5 pairs and each pair can contribute in 3 ways - First element selected or Second element selected or None is selected.
So total subsets = 3^5 = 243 ways (which includes null set too)

Let length of train is is ‘L’ km and speed ‘S’ Km/hr
L/X-11 = 20/3600 = 1/180
L/X = 9/3600 = 1/400
X = 400 L
180 L = X – 11
180L = 400L-11
220L = 11
L = 11/220 = 1/20 KM = 1000/20 =50 meters

1/x + 1/y = 1/n=> xy = nx + ny=> (x - n)(y - n) = n²
Now, n² must have 5 factors to get 5 ordered pairs=> n must be of form p², where p is prime number
Hence all primes less than 20

Let assume length of the train is ‘L’ and speed of train = a.
Speed of man 1 = b.
Speed of man 2 = c.
20 = L / a – b.
18 = L / a + c.
18a + 18c = 20a – 20b.
a = 10b + 9c.
Distance of two men = 600 x (a + c).
Time = 600(a+c) – 600(b+c) / (b+c)
= 600 ( a – b) / (b + c)
= 600 (10b + 10c – b) / (b + c)
= 5400 seconds
= 90 min (ans)