If you take a sheet of paper and mark it with a diagonal line, as in Figure A, you will find that when you roll it into cylindrical form, with the line outside, it will appear as in Figure B.

It will be seen that the spiral (in one complete turn) is merely the hypotenuse of a right-angled triangle, of which the length and width of the paper are the other two sides. 
In the puzzle given, the lengths of the two sides of the triangle are 40 ft. (one-fifth of 200 ft.) and 16 ft. 8 in. 
Therefore the hypotenuse is 43 ft. 4 in. 
The length of the garland is therefore five times as long—216 ft. 8 in. 
A curious feature of the puzzle is the fact that with the dimensions given the result is exactly the sum of the height and the circumference.