distance on horizontal=√(18^2+18^2)=18*√2 ft
distance on vertical=21 ft
∴θ=angle in between pole & cable=tan-1(18*√2/21)=50.479 degree
Σall horizontal force=0
1680=2T sinθ
∴T=1088.944 lb
Σall vertical force =0
R=2T cosθ [R= reaction force at A ]
∴R=1385.924 lb
How many components are there to the reaction at A (at most)? You ask if it is correct. But you could determine this yourself by recognising that there are at most 6 equilibrium equations for the whole thing...
(By the way your physicsp148.doc document has just one line and it is sloppy, or incorrect or inconsistent. If T is a force, why do the units have ft at the end?)