1, the number difference between two stacks of books is three, and the height difference is 88-86.5.

So the height of the textbook is (88-86.5)/3 = 0.5cm.

2. Because 86.5 is the height of the table and three books.

So the height of the table is 86.5-0.5×3=85 cm.

So the algebraic expression of the height of the textbook from the ground is 85+0.5xcm

3. There are 56 books, of which 14 is selected and the rest (56- 14) is selected.

According to the first question, the height of the textbook is 0.5 cm.

So the height of the remaining math textbooks from the ground is 0.5× (56-14)+85 =106 cm.