SOLUTION:
Let the cost of your lunch be represented by "x" and the cost of the lunch of your friend since it is $3 more than your would be "x + 3"
[tex]\begin{gathered} x\text{ + x + 3 = 15} \\ 2x\text{ + 3 = 15} \\ 2x\text{ = 15 -3} \\ 2x\text{ = 12} \\ x\text{ = }\frac{12}{2} \\ \\ x\text{ = 6} \end{gathered}[/tex]The amount you spent for lunch is $6.
