4. A baker had $3 \frac{3}{5}$ kilograms of walnuts. He bought another $2 \frac{1}{4}$ kilograms of walnuts. He kept all the walnuts equally in 3 containers. How many kilograms of walnuts were in each container?

Step 1 ：First, we need to add the initial amount of walnuts the baker had to the amount he bought. The initial amount of walnuts is \(3 \frac{3}{5} = 3.6\) kilograms and the amount he bought is \(2 \frac{1}{4} = 2.25\) kilograms. So, the total amount of walnuts is \(3.6 + 2.25 = 5.85\) kilograms.

Step 2 ：Then, we need to divide this total amount by the number of containers to find out how many kilograms of walnuts were in each container. The number of containers is 3. So, the amount of walnuts in each container is \(\frac{5.85}{3} = 1.95\) kilograms.

Step 3 ：Final Answer: Each container had \(\boxed{1.95}\) kilograms of walnuts.