Concept:Four numbers are in proportion when the ratio of the first to the second equals the ratio of the third to the fourth.Explanation:Let x be the number added to each.The new numbers become (10+x), (18+x), (22+x), and (38+x).Set up the proportion: 18+x10+x​=38+x22+x​.Cross-multiply: (10+x)(38+x)=(18+x)(22+x).Expand: 380+48x+x2=396+40x+x2.Cancel x2: 380+48x=396+40x.Simplify: 48x−40x=396−380⇒8x=16⇒x=2.Answer:2 is to be added.