Question

assuming that a person of a normal sight can read print at such a distance that the letters subtend an angle of 5' at his eye,find the height of letter that he can read a distance of 12m

Answer 1

Convert 5` into degrees = 5/ 60 degrees

Now replace it in the equation
tan (5/60) = PQ/12

PQ = 12 * tan (1/12)
= 12* 0.00145
= 0.0174 m =1.7cm

Value of tan(1/12) you can find using scientific calculator from google or it will be given in the question when asked in exam or log table will be provided.
Find 1/12 =0.083
From log table check tan(0.083)