To find the common difference in the arithmetic sequence, we subtract the first term from the second term.
The first term is \( \frac{3}{4} \), and the second term is \( \frac{6}{4} \).
The common difference \( d \) is calculated as follows:
\[ d = \frac{6}{4} - \frac{3}{4} = \frac{6 - 3}{4} = \frac{3}{4} \]
To confirm, we can also check the difference between the second term and the third term:
\[ d = \frac{9}{4} - \frac{6}{4} = \frac{9 - 6}{4} = \frac{3}{4} \]
Thus, the common difference in the arithmetic sequence is \( \frac{3}{4} \).