attempt to use tan, or sine rule, in triangle BXN or BXS (M1)

\({\text{NX}} = 80\tan 55^\circ \left( { = \frac{{80}}{{\tan 35^\circ }} = 114.25} \right)\) (A1)

\({\text{SX}} = 80\tan 65^\circ \left( { = \frac{{80}}{{\tan 25^\circ }} = 171.56} \right)\) (A1)

Attempt to use cosine rule (M1)

\({\text{S}}{{\text{N}}^2} = {171.56^2} + {114.25^2} – 2 \times 171.56 \times 114.25\cos 70^\circ\) (A1)

\({\text{SN}} = 171{\text{ }}({\text{m}})\) (A1)

Note: Award final A1 only if the correct answer has been given to 3 significant figures.

[6 marks]