Answer:
 (a)  P = 5.664e^(0.024t)
 (b)  7.74 million
Step-by-step explanation:
(a) We are given the population for t=7, so we can write the equation as ...
 P = 6.7·e^(0.024(t -7))
This can be put in the desired form by factoring out 6.7e^(-0.024·7):
 P = 6.7e^(-0.024·7)e^(0.024t)
 P = 5.664e^(0.024t)
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(b) Evaluated for t=13, this is ...
 P = 5.664e^(0.024·13) ≈ 7.74 . . . million