This is a level 3 question! Part a) should be easy enough.

For part b), when I drew ‘1 group’, that’s for 1 group of 4 pens and 1 pencil. However, it could be:
8 pens and 2 pencils (2 groups)
12 pens and 3 pencils (3 groups)
16 pens and 4 pencils (4 groups)... etc

We don’t know how many groups! Let it be x no. of groups. From there, we form equations and eliminate to solve.