Answer: 4.

Explanation:
Given : Jon and Lexi are playing a marble game.
According to their rules, 4 points are awarded for each red marble collected and 7 points are awarded for each blue marble collected.
Let r be the number of red marbles and b be the number of blue marbles.
Then , the expression represents Jon's total score if he has r red marbles and b blue marbles will be :-
