12. Mariam and Sana are excited that a new store just opened in town! They go together the first day it opens! Each time Mariam goes to the store she plans to
spend Rs. 30, and each time Sana goes to the store she plans to spend Rs. 50. A
few weeks from now, Mariam and Sana are surprised to find out that they have
spent the exact same total amount of money at the store. What is the least
possible number of times that Mariam has been to the store?