m denotes how much money each person contributes.
Let n be the number of friends.
Let 1 denote including yourself
Let T denote the total amount of money.
T = m(n+1)
If you have 4 friends,
T = m(4+1)
T = ($5.25)(5)
T = $26.25
Then they've spent $26.25 altogether (Includes yourself contributing)
