Circles and tangents! Need some help!

Hello there. I was trying to solve a problem that seems kinda easy, but
is not. I've been searching in books and with some teachers and no one
seems to know the answer. I hope someone out there knows it...

Here is the problem:

1) Let C be the circle given bu the equation:
x^2+y^2+4x-6y-12=0
Draw a tangential line of C which passes the point P(6,-1). The
distance between the point P and the point of tangency is?

The answer is square root of 55, but I do not know how to get there.

Since I do not have the point in which the line is tangent to the cirle
I cannot have the equation of the line and without the equation of the
line I am not able to get the intersection point between the line a
circle to apply of the distance between two points and be able to get
the result.
I've done inverse equations, bisectors, parallel and perpendicular
lines and everyhting but as long as I am not able to get the equation
of the line I cannot solve it.

If there is someone there that can help I will gladly appriciate.
Thank you!

.

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