Question 795664
This seems to be a possible Calculus, derivative problem.  I have not completed this question all the way yet, but my strategy seems to be:


The derivative of the upper branch of the circle's function would be y'={{{(-x)/sqrt(4-x^2)}}}.  The general point on this circle, for this tangent line, would be (x, {{{(-x)/sqrt(4-x^2)}}}).


The line x=4 would have a general point, (4,y).


Next in the process is to use the Distance formula between these two general points and equate distance to 6, and then solve for x.