Answer:
$1754.57
Step-by-step explanation:
We assume that Sara wants to make her deposits at the beginning of each 6-month period, so the formula for an annuity due is useful.
A = P(1 +r/n)((1 +r/n)^(nt) -1)/(r/n)
For A = 15000, r = 0.10, n = 2, this becomes ...
15000 = P·1.05(1.05^7 -1)/0.05 ≈ 8.54911P
P = 15000/8.54911 ≈ 1754.57
Sara needs to make semiannual deposits of $1754.57 to accumulate $15000 in 3 1/2 years.