Hello, magentarita!
The orthocenter is the intersection of the altitudes.
Did you make a sketch ??
Find the orthocenter of a triangle with vertices:
G(2,5), H(6,5), J(4,1) Code:

(2,5)  (6,5)
A o * * * * * o B
*  : *
*  : *
* : *
    + *  : *      
 * :*
 o C
 (4,1)

Recall that an altitude is perpendicular to the opposite side.
Since is horizontal,
. . we see the altitude from is the vertical line
The slope of is: .
Hence, the altitude from has slope: .
The equation of altitude from with slope
. .
The intersection of this altitude with the vertical line
. . is: .
Therefore, the orthocenter is