Lx = b h^3 /12
Ly= b^3 h/ 12
Where:
Lx= Area moment of inertia related to the x axis
Ly= Area moment of inertia related to the y axis
b= base = 3 cm
h= height = 8 cm
Replacing:
Lx = 3 (8)^3 / 12 = 3 (512) /12 = 128 cm^4
Ly= 3^3 * 8 / 12 = 27 (8) / 12 = 18 cm^4
Answer = 18 cm4