--Face Left ----- Face Right--
A-26 12 48 ----- 206 12 59
C-172 23 08 ---- 352 23 17
146 10 20 ---- 146 10 18

i have been told to work out the horizontal angle giving these figures using a calculator. The answers can be shown in red, however I am puzzled on how to find the answer using a calculator.

Could anyone help me with this please? Thanks.