Let n be the number of week
At nth week, Manuel has 250 + 150n
At nth week Felicia has 1650 - 200n
For them to have same amount, then;
250+150n = 1650 - 200n
Collect like term
150n + 200n = 1650 - 250
350n = 1400
Divide both-side of the equation by 350
n = 4
Therefore, they will have the same amount at the end of 4th week.