The formula to calculate the distance between two parallel lines \(Ax + By + C_1 = 0\) and \(Ax + By + C_2 = 0\) is:
\[
\text{Distance} = \frac{|C_2 - C_1|}{\sqrt{A^2 + B^2}}
\]
Substituting the values for the given lines \(3x + 4y - 9 = 0\) and \(3x + 4y + 10 = 0\):
\[
\text{Distance} = \frac{|10 - (-9)|}{\sqrt{3^2 + 4^2}} = \frac{19}{5}
\]
Thus, the correct answer is \(19/5\) unit.