Let x = cost of bill prior to tip
[tex] 12+x=58.25 [/tex]
[tex] x=46.25 [/tex]
So, we know that before a tip was paid that the cost of the meal was $46.25. If there were three people at the dinner and we are trying to find the average spent prior to the tip, we can just divide.
Let a = average each person spent
[tex] 46.25/3=a [/tex]
[tex] a=15.42 [/tex]
On average, prior to the bill, each person paid approximately $15.42.