Question 793000
It's all about tangents:
{{{drawing(300,300,-6,19,-3,22,
rectangle(0,0,1,1),line(-6,0,19,0),
line(0,0,0,16.55),
blue(line(0,16.55,18.38,0)),
green(line(0,16.55,12.38,0)),
red(line(-5.4,0,0,16.55)),
locate(-0.2,0,N),locate(-0.2,18,R),
locate(-5.6,0,C),locate(12.4,0,G),locate(18.4,0,H),
locate(15.2,1.9,42^o),locate(8.4,1.9,53.2^o),
locate(-4.8,1.3,x)
)}}} {{{NH=NG+6m}}}
{{{RN/NG=tan(53.2^o)=1.3367}}} (rounded)
{{{RN/NH=RN/(NG+6m)=tan(42^o)=0.9004}}} (rounded) 
So {{{(NG+6m)/NG=1.3367/0.9004}}} (approximately)
{{{1+6m/NG=1.4846}}} (approximately)
{{{6m/NG=0.4846}}}
{{{NG=6m/0.4846=highlight(12.38m)}}}
{{{NH=12.38m+6m=highlight(18.38m)}}}
And since {{{RN/NH=0.9004}}} (rounded) so {{{RN=(18.38m)*0.9004=highlight(16.55m)}}}
 
b) {{{tan((x))=RN/NC=16.55m/"5.4 m"=3.065}}} (rounded)
Since {{{tan(71.93^o)=3.065}}}, {{{highlight(x=71.9^o)}}} (approximately)