Will give brainliest to correct answer.

-- This is a right triangle.  We know that because that little box 
is drawn at the right angle (C). 

-- Since it's a right triangle, we can use the side lengths 
in trigonometry equations.

-- The drawing tells us the length of the side OPPOSITE
the unknown angle (the 3), and also the length of the side
ADJACENT to the unknown angle (the 6).

-- While we're saying "opposite" and "adjacent" to ourselves,
that reminds us that the tangent of an angle is the quotient of

(opposite side) / (adjacent side).

-- So we know that the tangent of the unknown angle is (3/6) or (1/2) or 0.5 .   

-- With our calculator, our slide rule, our general knowledge, or the
tables in our Handbook of Chemistry and Physics, we look up to
find what angle has a tangent of 0.5 .   It's 26.57° .