9x + 0 + 10x and 19x + 1 equivalent or not

What is the definition of exponential decay?

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

Me, the vertices of quadrilateral coat are c(2,0), o(7,0), a(7,2) and t(2,2). prove that coat is a rectangle.