Please help the use of Gap Difference for this question because I can only seem to resort to algebra which I know the kids are not supposed to use (though I have taught mine). 

Q: For Children’s Day, Miss Lim decides to give children pencils. 

If she gives each student 3 pencils, she will have 4 extra.

If she gives each student 4 pencils, she need 8 more pencils.

(a) How many students are there?

(b) How many pencils does she have now?