thank you the answers correct but i dont understand its 1/10 and not just 10 as t?For C:
the equation would be P=1000e^(1/10*ln(2.5)t
so you would simply to substitute t =23 since 1995 is start and 2018 is what you're finding (2018-1995) = 23 yrs into the equation to find P:
P = 1000e^(23/10*ln(2.5))
You use the value you get in d and then you would input that t value (t=25) into the differential equation dP/dt which would be k(1000e^(kt)) or kP and then you would just calculate the value of the rate of change.
dP/dt = k(1000e^25k) = 905
My maths might be a bit dodgy since its 11 here so I think someone here else could format this more nicely.
So B asks you to find k. Half of the salt left would mean that S at t = 3 would equal initial value of S divided by 2. To find initial value of S, make t = 0;