For I:
Let the present age of 'P' = x years
Present age of 'R' = 2x years
Sum of the present ages of 'Q' and 'R' = 36 X 2 = 72 years
Present age of 'Q' = (72 - 2x) years
Present age of 'S' = [(72 - 2x)/6] X 13 years
After eight years, the age of 'P' = (x + 8) years
After eight years, the age of 'T' = [(x + 8)/7] X 13 years
Present age of 'T' = [(x + 8)/7] X 13 - 8 years
Sum of the ages of 'P', 'S' and 'T = (40 X 5) - 72 = 128 years
x + {[(72 - 2x)/6] X 13} + {[(x + 8)/7] X 13} - 8= 128
x + (936 - 26x)/6 + (13x + 104)/7 - 8= 128
42x + 6552 - 182x + 78x + 624 - 336 = 128 X 42
62x = 1464
x = 1464/62
Therefore, I cannot be true.
For II:
Let the present age of 'P' = x years
Present age of 'R' = 2x years
Sum of the present ages of 'Q' and 'R' = 32 X 2 = 64 years
Present age of 'Q' = (64 - 2x) years
Present age of 'S' = [(64 - 2x)/6] X 13 years
After eight years, the age of 'P' = (x + 8) years
After eight years, the age of 'T' = [(x + 8)/7] X 13 years
Present age of 'T' = [(x + 8)/7] X 13 - 8 years
Sum of the ages of 'P', 'S' and 'T = (36 X 5) - 64 = 116 years
x + {[(64 - 2x)/6] X 13} + {[(x + 8)/7] X 13} - 8= 116
x + (832 - 26x)/6 + (13x + 104)/7 - 8= 116
42x + 5824 - 182x + 78x + 624 - 336 = 116 X 42
62x = 1240
x = 20
Present age of 'T' = [(x + 8)/7] X 13 - 8 = 44 years
Present age of 'S' = [(64 - 2x)/6] X 13 = 52 years
Difference = 52 - 44 = 8 years
Therefore, 'II' can be true.
For III:
Let the present age of 'P' = x years
Present age of 'R' = 2x years
Sum of the present ages of 'Q' and 'R' = 20 X 2 = 40 years
Present age of 'Q' = (40 - 2x) years
Present age of 'S' = [(40 - 2x)/6] X 13 years
After eight years, the age of 'P' = (x + 8) years
After eight years, the age of 'T' = [(x + 8)/7] X 13 years
Present age of 'T' = [(x + 8)/7] X 13 - 8 years
Sum of the ages of 'P', 'S' and 'T = (30 X 5) - 40 = 110 years
x + {[(40 - 2x)/6] X 13} + {[(x + 8)/7] X 13} - 8= 110
x + (520 - 26x)/6 + (13x + 104)/7 - 8 = 110
42x + 3640 - 182x + 78x + 624 - 336 = 110 X 42
-62x = 692
x = -692/62
Age cannot be negative.
Therefore, III is false
Hence, option 1 is correct.