The resultant is the vector sum of the sum of each component. The components are perpendicular, like an x-y graph. Since you only have two components altogether, your resultant is the sum of 50N along y, and 20N along x. It's given simply by
[tex]F_{res}=20 a_x + 50a_y [/tex]
where [tex]a_x[/tex] is the unit vector along x and [tex]a_y[/tex] is the unit vector along y. The magnitude of [tex]F_{res}[/tex] is given by the Pythagorean theorem as
[tex]|F_{res}|= \sqrt{20^2+50^2}=53.85N [/tex]
Its angle above the x-axis is given by the arctangent of the y-component divided by the x-component:
[tex]\theta = tan^{-1}( \frac{50}{20})=68.2 \deg [/tex]
