The third line in the Balmer series corresponds to an electronic transition between which Bohr's orbits in hydrogen?

The energy levels for a hydrogen-like species with atomic number $Z$ can be given by:

The kinetic energy of electrons emitted, when radiation of frequency $1.0 \times 10^{15} \ Hz$ hits a metal, is $2 \times 10^{-19} \ J$. What is the threshold frequency of the metal (in $Hz$)?
$(h = 6.6 \times 10^{-34} \ Js)$

Which of the following energy changes is less than the third Balmer transition in the $He^{\oplus}$ ion?

What is the ratio of time periods $(T_1 / T_2)$ in the second orbit of a hydrogen atom to the third orbit of a $He^{+}$ ion?

Calculate the wave number for the longest wavelength transition in the Balmer series of atomic hydrogen.