a=(209-7b)/3. When b=2, a=65, when b=5, a=58, when b=11, a=44, etc.,
The pattern is: b=2+3n, a=65-7m where m and n are positive integers.
We can tabulate these values:
a b
65 2
58 5
44 11
30 17
16 23
2 29
Note that apart from the number 2 for b, all even values for b have been omitted, because they are all divisible by 2, so are not prime. b=5+6k where k is a positive integer.
The only pair of primes is a=2 and b=29.