Sara is 3 years older than melissa. This means that Sara age is Melissa's plus 3. We have:
[tex]\text{sara}=\text{melissa}+3[/tex]Their combined age is 15, this means that the sum of their age is 15. We have:
[tex]\text{sara}+\text{melissa}=15[/tex]We can solve this for "melissa" by replacing the age of sara on the second equation by the first expression. We have:
[tex]\begin{gathered} \text{melissa}+3+\text{melissa}=15 \\ 2\text{melissa}=15-3 \\ 2\text{melissa}=12 \\ \text{melissa}=\frac{12}{2} \\ \text{melissa}=6 \end{gathered}[/tex]We can find Sara's age by replacing Melissa's age by 6 on the first expression.
[tex]\text{sara}=6+3=9[/tex]Melissa's age is 6 years old and Sara's age is 9 years old.
