Well, we know that the healthy option is $60 per week. We know a week is 7 days. In the fast food plan you spend $20 per day. It would be $20 x 7 is which would be $140. Since it's asking you what to save we have to subtract $140 - $60 which equals $80.
A rectangular prism is a cuboid so volume of cuboid is base area x height which is 5x5x12=300 volume of pyramid is 1/3 x base area x height = 5x5x6x1/3=50 thus volume outside pyramid and inside cuboid is 300-50=250
