Rearrange, differentiate, substitute in LZ's numbers.

When I was a kid I used to pray every night for a new bicycle.
Then I realised God doesn’t work that way, so I stole
one and prayed for forgiveness.

As the above two comments suggested, the gradient can be found by writing the curve in terms of functions y = f(x) and differentiating those functions. You could also use implicit differentiation here, which is especially useful when it's difficult to rewrite the function explicitly. According to the chain rule:

          d/dx[(x+3)2] + d/dx[(y-2)2] = d/dx[25]

2(x+3) + d/d(y-2)[(y-2)2]*d/dx[(y-2)] = 0

              2(x+3) + 2(y-2)*d/dx[y] = 0

I'm just curious but how old are you?

I can't ask in what grade you are, because the system is different here. I want to compare your educational system to mine.

i'm 17 years old and did differentiation/integration at 15, but did implicit differentiation only this year, if you want to know :/ we're a sucky country.

Differentiation and integration at 15 sounds pretty early to me.