Question 773827
Find slope of line AB. Call this value M.  
Now find {{{m=-(1/M)}}}.
Use point-slope form for a line and with point P(4,2) and the slope m, find the equation for the line which they define.
Use this equation with x=2 to find the value of k.



The point-slope form for a line is {{{y-y[0]=m(x-x[0])}}} or alternatively {{{y=m(x-x[0])+y[0]}}};
Do not confuse lower-case letters for variables with upper-case letters for variables.