Need help understanding the answer for this exercise

From Basic Kanji Book 2 Lesson 31. I really didn't know much about the entire thing so I just looked up the answers and the price one confuses me. Even knowing the answer, I have no idea how it got to that. Apparently, it's 178,900 yen. 先輩方、ご指導をください🙇🏻‍♀️

by happyhappychan