A photon has an energy of 2.93 ✕ 10-25 J. What is its frequency?

geno has given you the correct wavelength.  The frequency is obtained by dividing the energy by h.

 

$${\mathtt{frequency}} = {\frac{{\mathtt{2.93}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{\left(-{\mathtt{25}}\right)}}{\left({\mathtt{6.626\: \!069\: \!3}}{\mathtt{\,\times\,}}{{\mathtt{10}}}^{\left(-{\mathtt{34}}\right)}\right)}} \Rightarrow {\mathtt{frequency}} = {\mathtt{442\,192\,779.360\: \!155\: \!499\: \!731\: \!945\: \!2}}$$

frequency ≈ 4.422*10⁸ s^-1

.

E = (h·c)/λ

2.93 x 10^-25  =  (6.626 x 10^-34 · 2.998 x 10^8) / λ

2.93 x 10^-25 · λ  =  (6.626 x 10^-34 · 2.998 x 10^8) 

λ  =   (6.626 x 10^-34 · 2.998 x 10^8) / ( 2.93 x 10^-25 )

λ   =  6.78 x 10^-1 m