Answer:
Mark is 9 and his brother is 14.
The expression for Mark: 23 - 9 = 14
The expression for his brother: 23 - 14 = 9
Step-by-step explanation:
We know that 14 is 5 more than 9, and Mark is the younger one so he would be 9 and his brother 14. 9 + 14 also equals 23, so thats how you know you have the right answers.