Explanation:
if I understand this correctly this is a right-angled triangle with the height 12.
x is the segment of the baseline left of the height ?
16° is the angle at the bottom right corner ?
the angle at the bottom left corner is (the sum of all angles in a triangle is always 180°)
180 - 90 - 16 = 74°
and then the height 12 is
sin(74)×upper left side
upper left side = 12/sin(74) = 12.48359323...
and now we can solve with Pythagoras for x using the left smaller triangle
upper left side² = 12² + x²
x² = upper left side² - 12² = 155.8400999... - 144 =
= 11.84009994...
x = 3.440944629...
if x is meant to be the whole baseline, then you need to do the same calculations for the right smaller triangle to get the length of the right segment. and then you need to add both numbers.
height 12 = sin(16)×upper right side
upper right side = 12/sin(16)
upper right side² = 12² + right baseline segment²
...