Final answer:
Both 'a' and 'b' are the prime number 149, so the relation between them is 'a' is equal to 'b'.
Step-by-step explanation:
If 'a' is the greatest prime number less than 150 and 'b' is the smallest prime number greater than 140, to find the relation between 'a' and 'b' we need to identify these prime numbers first.
For 'a', the greatest prime number less than 150 is 149. For 'b', the smallest prime number greater than 140 is 149 as well. This means that 'a' is equal to 'b', since they are both the same prime number.
Thus, the relation between 'a' and 'b' is 'a' = 'b' or in other words, they are equal to each other.