SOLUTION
Given:
Jonathan sells 3 times as many computers as his friend Mark. If the difference in their sales is 28, how many computers did each sell?
[tex]Let\text{ the number of computers sold by Jonathan be j, and that of Mark be m;}[/tex][tex]\begin{gathered} From\text{ the given statement;} \\ j=3m----(1) \\ j-m=28---(2) \\ Substitute\text{ j=3m into equation \lparen2\rparen} \\ 3m-m=28 \\ 2m=28 \\ m=\frac{28}{2} \\ m=14 \\ Substitute\text{ m=14 into equation \lparen1\rparen;} \\ j=3(14) \\ j=42 \end{gathered}[/tex]
Final answer:
[tex]\begin{gathered} Jonathan\text{ sold 42 computers.} \\ Mark\text{ sold 14 computers.} \end{gathered}[/tex]