The answer is 33.25 days
using the general formula for growth:
A = Pe^(rt)
get first the value of r
2 = 1e^(2.5r)
ln 2 = ln e^(2.5r)
r = 0.277
Then use this rate to solve for the main problem:
10000 = 1e^(0.277xt)
solving for t using the same procedure above, we will get:
t = 33.25 days