You say "the tables" as if we are looking at them too, or all tables have the same contents.
if i was using my tables (Tables and formulae for UK actuarial exams) i would use the following relationship:
This can be used to re-express your gamma probability as a chi-square probability. Chi-square distributions are tabulated.
If this isn't familiar, I assume your professor showed you one before giving you the question? how did he do it?