Answer:
about 1.14%
Step-by-step explanation:
Assuming you can redeem the T-bill for $100 at the end of the period, the interest rate can be found from the formula for simple interest:
I = Prt . . . . where P is the principal invested, r is the annual rate, and t is the number of years.
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Here, we have ...
(100 -99.44) = 99.44·r·(180/365) . . . . held for a fraction of a year
0.56×365/(99.44×180) = r ≈ 0.0114195 ≈ 1.14% . . . . divide by the coefficient of r
Your return would be about 1.14%.