This Application Problem is a part of the Lesson 15, Unit 2, Grade 1. Julian has 7 markers. His mother gives him 8 more. He loses 9 markers. How many does he have left? In the Student Debrief, students can discuss their drawings and number sentences and share various strategies, one of which may be decomposing 15 into 10 and 5 and taking 9 from 10.