13. 
Determine the height of a donkey. 

What is the height of a donkey, which is 8 feet less than a elephant has, and the height of a elephant is 3 times more than the height of a donkey? 



Explanation:
x = y  8; y = 3x. Therefore: x = 3x  8; 2x = 8. Hence: x = 4.


