Please help me In how many ways can we give six identical pens to three students

Please help me In how many ways can we give six identical pens to three students (note that a student can get zero pens)
Let A be a set of natural numbers from 1 to 10. How many ordered triples (x, y, z) are there such that x belongs to A, y belongs to A and z belongs to a. Also x

In an arithmetic progression, a5+a8+a11=28, and a14+a17+a20 =44. Find common difference.