6/7 + 21/10

Given the fractions:
\frac{6}{7} and \frac{21}{10}

Step 1: Find the common denominator:
The least common multiple of 7 and 10 is 70.

Step 2: Convert each fraction to have the common denominator:
\frac{6}{7} = \frac{6 \times 10}{7 \times 10} = \frac{60}{70}
\frac{21}{10} = \frac{21 \times 7}{10 \times 7} = \frac{147}{70}

Step 3: Add the fractions:
\frac{60}{70} + \frac{147}{70} = \frac{60 + 147}{70} = \frac{207}{70}

Step 4: Simplify the fraction (if possible):
\frac{207}{70} is already in its simplest form.

Therefore, the answer is:
\frac{207}{70}