Here are 2 ways of solving this problem.
1) The angle the triangle's vertical leg makes with the dotted line is 90 degrees.
90 - 28 = 62
The triangle's left upper angle is 62 degrees.
For the 62-deg angle, 350 ft is the adjacent leg.
The hypotenuse is x.
The trig ratio that relates the adjacent leg to the hypotenuse is the cosine.





Answer x = 745.5 ft
2) The dotted line has an arrow head. The triangle's horizontal leg also has an arrowhead. That means that the horizontal leg of the triangle and the dotted line are parallel. By alternate interior angles, the lower right angle of the triangle is also 20 deg.
For the 28-deg angle, the 350 ft leg is the opposite leg.
The hypotenuse is x.
The trig ratio that relates the opposite leg to the hypotenuse is the sine.





Answer x = 745.5 ft
As you can see, both methods give the same answer.