You are hiking along the edge of the Green River (which is running straight in the area of interest). Straight across from you on the opposite shore there is a particularly noticeable boulder at the edge of the river. You walk 120 feet along the shore of the river, and now the line from you to the boulder makes an angle of $35^\circ$ with the edge of the river. You whip out your trusty scientific calculator and deduce that the width of the river at this point is feet.
Hint: Draw a picture. "Straight across" means that the line from you to the boulder forms a right angle with the shore of the river.