You are towing a trailer on a divided highway that is posted at 65 mph. How fast may you drive?

Why

Towing changes your speed limit, not only your lane. The handbook puts vehicles towing trailers at 55 mph, the same ceiling it puts on a two-lane undivided highway, and that holds even where the posted maximum for everyone else is 65. So the number on the sign is not yours to use. Forty-five mph is not a limit the handbook sets for towing anywhere. There is a lane rule that travels with the speed rule: while towing a vehicle or trailer your place is the far-right lane, or whichever one is signed for slower traffic, and where nothing is marked and there are four or more in your direction, you may only use the two closest to the right edge.