How can you use greatest common factor and least common multiple to solve problems

Which graph represents 2x-5y< 15

In the image, point a marks the center of the circle. which two lengths must form a ratio of 1 : 2? (options are in the images since thought they were harmful phrases)

Ahomeowner plans to hang wallpaper on one wall of a bedroom that is 10 feet long if a stripe of wallpaper is 20 inches wide and stripes or hung vertically how many stripes on wall paper with the homeowner required