3x10^9 m/s divided by 3x10^15 Hz ... can y’all help m!!

The content of manganese (mn) in steel was determined spectrophotometrically and with the use of the standard addition method. an unknown sample of mn from a digested steel sample gave an absorbance of 0.185 when analyzed spectrophotometrically. when 5.00 ml of solution containing 95.5 ppm mn was added to 50.0 ml of the unknown steel solution (digested sample), the absorbance was 0.248. calculate the concentration, in parts-per-million (ppm), of mn in the digested steel sample solution.

Why is the melting of ice a physical change ?

What is the value of the standard enthalpy of formation of an element in its most stable form?