Solution: (1) Let the height of the desk be acm and the thickness of each book be bcm. ..

Then 3b+a=87. 76b+a=90.4。

The solution is a=85b=0.9.

The maximum height of this pile of textbooks from the ground is 85+0.9x

(2) When x=60- 18, 85+0.9x = 122.8 (cm).