As I said, you can just as easily make your own problems and check them on a calculator.
It would be hard to find a site that meets your particular desires when you haven't given an example of how complicated an expression you want, as I requested. My idea of "simple" may not be your "simple"! And the same is true of any site. There may well be such a site, but you have to judge whether it does what you want.
I just did a Google search for "arithmetic problem generator" and found sites such as
https://www.wolframalpha.com/problem-generator/ and many others that you can look through.