A photograph measuring 4 inches wide and 5 inches long is enlarged to make a wall murl if the murl is 80 inches wide how long is the murl?

If the photograph is 4" wide and the mural is 80" wide then the scale is 4:80 which simplifies to 1:20. That is, 1" on the photograph is represented by 20" on the mural.

If the photograph is 5" long, then the equivalent length of the mural is 5 x 20 =100"