Answer:
1.6 x 10⁻⁶ J/m³
Step-by-step explanation:
I = Intensity of electromagnetic radiation = 475 Wm⁻²
U = average total energy density of electromagnetic radiation
c = speed of electromagnetic radiation = 3 x 10⁸ m/s
Intensity of electromagnetic radiation is given as

Inserting the values

U = 1.6 x 10⁻⁶ J/m³