After trying all for stopping  builtin Apache on my computer (actually OS X 10.11.6 El Capitan) It was still keep saying “port 80 was using by another application” when I start the MAMP (MAMP Pro 3.5)

Even after stopping apache with;

And moreover killing the process;

At the same time by checking the actual working PHP engine with;

 

The only solution that I could find was;

Restart your Mac if needed.

Then MAMP fortunately turned to normal.