Question

number of numbers of the form 30a0b03 where a,b are digts which are divisible by 13 is

Answer 1

can you please explain this question , as a and b cannot be digits as any single digit is not divisible by 13
and if they are

Answer 2

For divisibility by 13 refer:
http://en.wikipedia.org/wiki/Divisibility_rule#Divisibility_by_13

∴ set of (a,b) such that 30a0b03 is divisible by 13
={ (a,b) : 6+3a-4b=13n ; n∈N∪{0} }
where a,b are digits

You can do trial and error from here.