Rina purchases 4 notebooks and 6 pens for ₹170. Amit purchases 6 notebooks and 4 pens for ₹180. (Ignore Rina's separate payment of ₹30 for a file.) Assuming every notebook costs ₹n and every pen costs ₹p, find the price of one notebook.
a) ₹18
b) ₹22
c) ₹15
d) ₹20