Need some help w/this equation please

Julius sold five times as many computers as sam sold last year. in total, they sold 78 computers. how many computers did julius sell?

Aplane intersects a pris paralel to the base of the prism. the cross section is a polygon wth eight sides. how many sides does the base of the prism have? a. 10 b. 8 c. 7 d. 9

How can constraints be used to model a real-world situation?