Well I am not pretty sure if it is correct but I think this:

1001 is divisible by 7, so we get 1001, 2002,..., til 9009 that is divisible by 7, so the only palindromes we can make from that is if we add 770, so we get a total of 9+9 that this is 18

So we have 18 numbers (1001, 1771,...)

I hope u understand it