This Application Problem is a part of the Lesson 14, Unit 4, Grade 2. The total length of a red string and a purple string is 73 cm. The red string is 18 cm long. How long is the purple string? This Application Problem allows students to practice the skill from Lesson 13. In order to keep their work simple, perhaps draw the tape diagram together, and then let them solve the subtraction and write their solutions independently.