It is given in the question that
Ann, Chang, and Kareem sent a total of 89 text messages over their cell phones during the weekend. Ann sent 9 fewer messages than Chang. Kareem sent 3 times as many messages as Ann.
Let number of messages Chang sent be x. And Ann sent 9 fewer than Chang, so Ann sent (x-9) messages. And Kareem sent 3 times as many messages as Ann, so Kareem sent 3(x-9) messages.
And the total messages are 89. That is

Combining like terms

So Chang sent 25 messages, Ann sent

And Kareem sent

Well, if we take 68.73 as the 100%, how much is 12 of it in percentage?
well

solve for "x"