The roof is made up of two mirred right triangles which are congruent. We can find the width by finding the width of one of the triangles then doubling the answer to get the width of the entire roof.
We are given that the slope (rise over run) is 5/12 which means that for every 5 feet of height there is 12 feet of width. We can use this ratio to find the width of one triangle given the height of 8 by setting up the following proportion:
5/12 = 8/x
Solve for x by cross multiplying:
5x = (12)(8)
x = (12)(8)/5
x = 19.2 feet
Multiply by 2 to get the entire width:
(19.2)(2) = 38.4 feet
The answer is 38.4 feet