Best to use a Douglas Navigational Protractor. In this example, the strike is 124 o or 304 o . More Stike Lines Draw additional strike lines, at some sensible contour interval. Call this Line 3. This is the trace of the maximum slope or dip of the plane on the map view.
True dip is always perpendicular to strike in map view.
Steps One through Four are here . Steps Nine through Twelve are here .