To save money, you put $200 in your bank account each week. After saving for 4 weeks, you have $1,700$ dollars in your account. Which equation models your savings account balance at the end of each week?

Let's say the savings in your account are given by $V, the number of weeks by n and the starting balance by $x:
V = x + 200n

Now if after saving for 4 weeks you have $1700 in your account, then:
1700 = x + 200*4
1700 = x + 800
x = 900, thus your starting balance is $900

Using this information we can now write up the general equation for the savings at the end of each week:
V = 900 + 200n