We already know that Jackson biked k kilometers.
Maria biked 8 more kilometers than Jackson, which means that she biked
[tex]k+8[/tex]Peter biked 2 fewer kilometers than Jackson, which means that he biked
[tex]k-2[/tex]To get the total all of them biked, we add those expressions together.
[tex]k+(k+8)+(k-2)[/tex]