Resolve forces perpendicular to the plane:

\(T \sin 60 + R = 25 \cos 20\)

Resolve forces parallel to the plane:

\(T \cos 60 = F + 25 \sin 20\)

\(T \cos 60 + F = 25 \sin 20\)

Using the friction formula \(F = \mu R\):

\(T \cos 60 = 25 \sin 20 + 0.3(25 \cos 20 - T \sin 60)\)

Substitute \(F = 0.3R\) into the equation:

\(T = \frac{25 \sin 20 + 0.3 \times 25 \cos 20}{\cos 60 + 0.3 \sin 60}\)

Calculate the values:

\(T = 6.26\) N (least value)

\(T = 20.5\) N (greatest value)