X+2X=840
3X=840
X=280
2. let Xiao Ming be X.
3X=X+22
2X=22
X= 1 1
3. I saw it myself ~
Suppose Xiaoming has x books.
x+5=50÷2
x=20
Or suppose Xiaoxiao has X books.
x-5 = 50 \2
x=30