A right triangle has an angle that equals 90°. Complementary angles equal 90°. Therefore, if you add these two angles, you will know whether or not △ABC is a right triangle. Triangle △ABC is broken up into two angles, m∠ABD and m∠DBC. When the measures m∠ABD and m∠DBC are added together, they equal 90°, and thus, form a complementary angle.
The next larger thousandth is 36.994 . The next smaller thousandth is 36.992 . Neither of those is any nearer to 36.993 than 36.993 already is.
The last '3' at the end of 36.993 is in the thousandths' place. There is no more piece of another thousandth after it. So 36.993 is already on a complete thousandth, and there's no rounding required.