Raj is making korma for a party. He puts 25 g of curry powder

6.3 trees.

Step-by-step explanation:

We have been given that Meryl needs to cut down 10.5 trees for every 5 cabins she builds.

Let us find the number of trees Meryl needs to cut down to build 1 cabin by dividing 10.5 by 5.

Now let us multiply 2.1 by 3 to find the number of trees Meryl needs to cut down to build 3 cabins.

Therefore, Meryl needs to cut down 6.3 trees, if she builds 3 cabins.