I think the answer is 175.
Hopefully this helps.
The point (2, 5) is not on the curve; probably you meant to say (2, -5)?
Consider an arbitrary point Q on the curve to the right of P,
, where
. The slope of the secant line through P and Q is given by the difference quotient,

where we are allowed to simplify because
.
Then the equation of the secant line is

Taking the limit as
, we have

so the slope of the line tangent to the curve at P as slope 2.
- - -
We can verify this with differentiation. Taking the derivative, we get

and at
, we get a slope of
, as expected.
You can solve a system of three equations by multiplying each equation by a number that allows you to add or suvtract the same equation together by eliminating the x or y variable