Regarding the d[t] - d hint and finding an offset.
We know the t we want is 4, and we know t=6 which is 61 (for c=145).
The pattern of dt - d is represented by the function 2*t^2 - 12. Similar to the normal equation for d. That function is negative for 1, 2 but for it's not for 3. What if that's the offset?
6 - 2 = 4.
Maybe the t-1 where d[t] - d is the first positive number represents (e, n)s t?
It appears to work for the numbers I checked