Answer: b) 18.37
Step-by-step explanation:
Since the intial t-value is 1960 and the final t-value is 1990, then t = 30
[tex]P(30)=\dfrac{100}{1+400\cdot e^{-0.15(30)}}\\\\\\.\quad =\dfrac{100}{1+400\cdot e^{-4.5}}\\\\\\.\quad =\dfrac{100}{1+400(0.0111)}}\\\\\\.\quad =\dfrac{100}{1+4.4436}}\\\\\\.\quad =\dfrac{100}{5.4436}}\\\\\\.\quad =\boxed{18.37}[/tex]
