Answer:
x = 1/20 y^2 
Explanation:
This is a rightward opening (sideways ) parabola 
Directrix = x = -5 
Distance formula form point x,y to directrix and focus are equal: 
(x - -5)^2 = (x-5)^2 + y^2 
x^2 + 10x + 25 = x^2 - 10x + 25 + y^2 
20x = y^2 
x = 1/20 y^2