What is the weight of 8 meter x 1.5 meter 5millimeter steel plate?

Answer 1

-- The volume of that plate is (8) x (1.5) x (0.005) = 0.06 meter3 = 60,000 cm3

-- The density of steel varies based on the alloying constituents but
usually ranges between 7,750 and 8,050 kg/m3 (484 and 503 lb/cu ft),
or 7.75 and 8.05 g/cm3 (4.48 and 4.65 oz/cuin).

-- So, depending on its composition, the mass of your plate is 465 - 483 kg,
and its weight is 1,025.1 - 1,064.8 pounds. (rounded)