I can't give an exact number if the original velocity of ds-1 is not given. In that case, the final answer should just be in terms of an equation. Let's denote the original velocity to be v₀ and the days to be d.
Part a.)
v = v₀ + 9.23d
3440 = v₀ + 9.23d
9.23d = 3,440 - v₀
d = (3,440 - v₀)/9.23
Part b.)
The acceleration is the change in velocity per unit time. So, that would be 9.23 m/s per day. Since there are 86,400 s in a day:
a = 9.23 m/s / day * 1 day/ 86,400 s
a = 0.0001068 m/s²