solution:
R = {(a, b) : a = b – 2, b > 6}
(A) Incorrect : Value of b = 4, false.
(B) Incorrect : a = 3 and b = 8 > 6
a = b – 2 => 3 = 8 – 2 and 3 = 6, which is bogus.
(C) Correct: a = 6 and b = 8 > 6
a = b – 2 => 6 = 8 – 2 and 6 = 6, which is valid.
(D) Incorrect : a = 8 and b = 7 > 6
a = b – 2 => 8 = 7 – 2 and 8 = 5, which is false.
Thusly, alternative (C) is right.