So, 260 degrees is in the 3rd quadrant, only 10 degrees away from being straight down at 270 degrees....if you have a xy axis, and draw a line segment from the origin into the 3rd quadrant, then at the endpoint of that segment, draw back up to the x-axis, your reference angle is the angle that the line segment makes with the x-axis (in this case, the negative portion of the x-axis), which is 80 degrees....since 260 degrees is 80 degrees past 180.
So your answer is 80 degrees.
Hope this helps,
Brian