Final answer:
The trend projection for period 15 using the given linear trend equation Tt = 28.5 + 0.75t is c. 39.75.
Step-by-step explanation:
The linear trend equation given is Tt = 28.5 + 0.75t, where t represents the time period. To find the trend projection for period 15, we substitute t with 15 into the equation:
T15 = 28.5 + 0.75(15)
Now performing the calculation:
T15 = 28.5 + 11.25 = 39.75
Therefore, the trend projection for period 15 is 39.75, which corresponds to option c.