Answer:
12.62
Step-by-step explanation:
imagine a circle with the center at the corner (let's call it A) with the 31 degree angle. the radius is AB.
so,
x = sin(31)×AB
and
21 = cos(31)×AB
therefore,
AB = 21/cos(31) = 24.4993...
=> x = sin(31)×24.4993... = 12.62 (12.61807...)
