True course = 260 degree. So, course is SW 80 Degree (S 80 W).

Sinco = (Dep / Dist)
Cosco = (dlat / Dist)
Tanco = (Dep / dlat)
Dep = (dlong * Cos m’lat)

Find out dlat in degree. How?
We know, Cosco = (dlat / Dist)
So, dlat = Dist * Cosco (Suppose our dist is 275.022 NM)
So, Input data in calculator like that, 0° 275.022° * cos 80° = 0° 47.76′ S

Or, 275.022 * Cos 80° = 47.757
47.757 / 60 = 0° 47.76′ S

To get meridional parts, subtract the meridional parts if latitude are of the same sign.

Find out dep in NM. How?
We know, Sinco = (Dep / Dist)
So, Dep = Dist * Sinco (Suppose our dist is 275.022 NM)
So, Input data in calculator like that, 275.022 * sin 80° = 270.86′

Find out dlong in degree.

Dep = dlong * cos m’lat
M’lat = Initial lat – (d’lat/2)

If Initial lat and Final lat same name = dlat (-)
If Initial lat and Final lat opposite name = dlat (+)
(Opposite formula with dev and variation – CE)

And, If Initial lat and dlat same name = Final lat (+)
And, If Initial lat and dlat opposite name = Final lat (-)

If Initial lat and Final lat same name, mlat = (1st + 2nd)/ 2
If Initial lat and Final lat opposite name, mlat = (1st – 2nd)/ 2