Fifteen equals three more than six times a number

Noor brought 21 sheets of stickers. she gave 1/3 of a sheet to each of the 45 students at recess. she wants to give teachers 1 1/2 sheets each.

Write an equation for the function that includes the points (1,4/5) and (2,2/3)

What is the best way to answer questions with a x expression in the question. for example 3x + 10x=?