The midway point between 30W and 20W is 25W.
At 60S the departure between 30W and 25W is 150 nm.
We can now draw a triangle with a horizontal side 60S 30W to 60S 25W. The length of this line will be 150 nm.
The second side is a vertical line from 60S 25W down to the unknown position south of 25W.
The third line is the hypotenuse form 60S 30W to the unknown position south of 25W.
The internal angle between the hypotenuse and the horizontal side is the conversion angle based on going from 60S 30W to 25W.
This angle = 0.5 x 5 degrees x Sin 60 = 2.165 degrees.
The tangent of this angle is the vertical side divided by the horizontal side.
Tan 2.165 = Ch lat / 150 nm
Rearranging this gives Ch lat = Tan 2.165 x 150 = 5.67 degrees.
This means that the change of latitude between 60S 30W and the unknown position south of 25W is 5.67 degrees. This makes the new latitude 60 degrees 5.67 minutes south. The closest option to this is 60°06’S