Mark is buying supplies for his students. He is buying a notebook (n) and a pack of pencils for each of his 25 students. Each pack of pencils costs $1.25. If Mark's total cost is $156.25, which of the following equations can be used to find how much each notebook cost? Select two that apply.

a) 25(n) + 31.25 = 156.25
b) 1.25(n) + 25 = 156.25
c) 25(n) = 156.25 + 31.25
d) 25(n) = 156.25 – 31.25