a. $\frac{-5}{6}+\frac{3}{6}=$

Step 1 ：Given the fractions \(-\frac{5}{6}\) and \(\frac{3}{6}\), we are asked to find their sum.

Step 2 ：Since the denominators of the fractions are the same, we can directly add the numerators. The operation is -5 + 3.

Step 3 ：Performing the operation, we get -2.

Step 4 ：Thus, the sum of \(-\frac{5}{6}\) and \(\frac{3}{6}\) is \(-\frac{2}{6}\).

Step 5 ：Simplifying the fraction \(-\frac{2}{6}\) to its lowest terms, we get \(-\frac{1}{3}\).

Step 6 ：So, the final answer is \(\boxed{-\frac{1}{3}}\).