To expand the expression \(\frac{9}{4}(5x + \frac{3}{4})\), we apply the distributive property:
\[ \frac{9}{4}(5x) + \frac{9}{4}\left(\frac{3}{4}\right) \]
Calculating each term:
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For the first term: \[ \frac{9}{4} \cdot 5x = \frac{45}{4}x \]
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For the second term: \[ \frac{9}{4} \cdot \frac{3}{4} = \frac{27}{16} \]
Now, combine both terms:
\[ \frac{45}{4}x + \frac{27}{16} \]
Thus, the expanded expression is:
\[ \frac{45}{4}x + \frac{27}{16} \]
So the correct answer is:
a. \(\frac{45}{4}x + \frac{27}{16}\).