Answer:

So we have two points for the solution:
Explanation:
For this case have the following equation given:

And if we see this equation ahve the general form of a circle given by:

Where the center os (0,0) and the readius

For this case we have a point given (2.1,y) and we are interested in find the y missing coordinate, so we jjust need to replace the point into the equation and we got:

Now we can solve for y like this:

And now we can take square root on both sids and we got:

So we have two points for the solution: