Lets call the amount of weeks till they save the same amount of money x. i.e , it will take them weeks to save the same amount.
Brian would have saved 20+3x
Marquise would have saved 10+5x
Lets equate them because they are the same amount of money, thus
20 + 3x = 10 + 5x
20 -10 = 5x -3x
10 = 2x
x = 5 weeks
Therefore it would take 5 weeks.
Option D