In a particular instance, if three lines of Paschen series are observed in the emission spectrum of hydrogen total number of lines in the observed spectrum will be 

Lines in Paschen series in Hydrogen spectrum are due to electronic transition  n > 3 to n = 3. Three lines are due to transition from 6 to 3; 5 to 3 and 4 to 3. Highest energy level is n = 6 and total number of spectral lines recorded = $\frac{6(6-1)}{2}=15$