Answer:
week 4
Step-by-step explanation:
With Ben saving up $150 every week, he'll have $850 by week 4 because, $150 times 4 is $600, plus the $250 that he started with equals $850. Tim will also have $850 by week 4 because $200 times 4 equals $800. $800 minus the $1650 that he started off with equals $850.