Matthew and some friends are going to a concert. They hire a car service for $75 to drive them to a
restaurant for dinner and then the concert. They divide the $60 cost of the dinner equally. However, since
Matthew's dad provided concert tickets for the group, the friends agree that Matthew doesn't have to help pay
for the car service. The friends divide this cost equally among themselves. If each friend spends a total of $25,
how many friends went to the concert with Matthew?