Answer:
$6,506.51
Explanation:
Recall that increasing an amount C in x% is equivalent to multiply it by (1+x/100)
As we have 4% APR, the monthly interest would be (4/12)% = 0.04/12
Month 0 (first payment)
$250
Month 1

Month 2

Month 3

Month 24 (2 years)

The sum

is the sum of the first 24 terms of a geometric sequence with common ratio
which is

so, after 2 years the saving balance is
250*26.02603071 = 6,506.50767= $6,506.51 rounded to the nearest cent.