Note that you were given only one energy state. If you consider two energy states, from
$E_1 - E_4 = color(blue)(DeltaE)$
$= -2.18xx10^(-18) "J"(1/n_f^2 - 1/n_i^2)$
$= -2.18xx10^(-18) "J"(1/1^2 - 1/4^2)$
$= -2.18xx10^(-18) "J"(15/16)$
$=$ $-color(blue)(2.04xx10^(-18) "J")$
After you obtain the energy, then you can realize that that energy has to correspond exactly to the energy of the photon that came in:
$|DeltaE| = E_"photon" = hnu = (hc)/lambda$
where
$=> color(blue)(lambda) = (hc)/(E_"photon") = ((6.626xx10^(-34) "J"cdot"s")(2.998xx10^(8) "m/s"))/(2.04xx10^(-18) "J")$
$= 9.720 xx 10^(-8)$ $"m"$
$=$ $color(blue)("97.20 nm")$