Since this is a right triangle, we can use one of the three main trigonometric functions: sine, cosine, tangent.
Remember: SOH-CAH-TOA
From the angle, we know the opposite side and want to figure out the adjacent side. Therefore, we should use the tangent function.
tan(35) = 6/RS
RS = 6 / tan(35)
RS = 8.6
Hope this helps!