Atomic Structure

$a, b, c, d$ are electromagnetic radiations. Frequencies of $a, b$ are $3 \times 10^{15} \mathrm{~Hz}, 2 \times 10^{14} \mathrm{~Hz}$, respectively, whereas wavelength of $c, d$ are $400 \mathrm{~nm}, 750 \mathrm{~nm}$, respectively. The increasing order of their energies is