If Youyou and Huanhuan have enough money to buy this book, then I will buy this book.

Suppose Cong Cong brought X yuan, obviously Y yuan, and the book price was Z yuan.

Youti

X+3=Z 1

y+4 = Z ^ 2

x+Y = Z ^ 3

Add 1+2.

X+Y+7=Z+Z 4

Play 4-3

Get Z=7.

So the story book 7 yuan