i suppose t is the time in years.

in 1996, the company sold 300,000 units, that means when t = 2, s = 300,000. now we can use this to solve for k

=> 300000 = 500000/(1 + 0.6e^(2k))

=> 300000(1 + 0.6e^(2k)) = 500000

=> 1 + 0.6e^(2k) = 500000/300000 = 5/3

=> 0.6e^(2k) = 5/3 - 1 = 2/3

=> e^(2k) = 2/3*10/6 = 10/9 ...................0.6 = 6/10 so i multiplied both sides by 10/6

now we take the log of both sides

=> lne^(2k) = ln(10/9)

=> 2k*ln(e) = ln(10/9)

=> 2k = ln(10/9) ........................lne = 1

=> k = ln(10/9)/2 = 0.0527

so the complete model is s = 500,000/(1 + 0.6e^(0.0527t))

in 1999, t = 5b) estimates sales in 1999

=> s = 500,000/(1 + 0.6e^(0.0527(5)))

=> s = 500000/(1 + 0.7809)

=> s = 280756.92 units