how to add tennis court for the residents?

I have the same problem. I am stuck at "Add 1 tennis court for 4 residents" No matter how many courts I add it doesn't work. Please help !

You just need to add 1 tennis court.
But it has to cover 4 residents, so you'd better to add a tennis court in the middle of residential area.
First, put a tennis court in decent area, then click the tennis court, a covered residents would be showed in green.