Hi there!
To break down this answer into more understandable parts, is shown below:
Three tens is equal to the number 30, because when you multiply three by ten, it makes thirty.
Ten ones is equal to the number 10, because when you multiply ten by one, you end up with ten.
Now, all you have to do is add the two numbers with a calculator to get your answer. In this case, we're left with 40 as our solution.
I hope this helped you out! ^-^