Answer:
60
Step-by-step explanation:
You need to think of it as an equation system.
First of all, let's call A the apple trees, P the pear trees and V the avocado's trees.
As for every 3 pear trees we have 4 apple trees, it can be written as:
4A = 3P
Then, we can clear the pears dividing both sides by 3:
4A/3 = 3P/3
(4/3)A = P
This is, we have one pear tree for every 4/3 apple trees.
Then we go to the other relation. For every 5 pears trees there are two avocados trees:
2V = 5P
As we want the ratio of avocados to apples we can replace the pear trees by it's expression depending on A:
2V = 5 ((4/3)A)
2V = (20/3) A
Multiplying both sides by 9 we make appear our 18 avocados trees:
2V *9 =( 20/3) A * 9
18 V = 60 A
So, for 18 avocados trees we have 60 apple trees.