Length of painted cardboard = 8 cm and breadth of painted card = 5 cm

Since, there is a margin of 1.5 cm long from each of its side.

Therefore reduced length

= 8 – (1.5 + 1.5) = 8 – 3 = 5 cm

And reduced breadth

= 5 – (1.5 + 1.5) = 5 – 3 = 2 cm

Therefore Area of margin = Area of cardboard (ABCD) – Area of cardboard (EFGH)

= (AB x AD) – (EF x EH)

= (8 x 5) – (5 x 2)

= 40 – 10

= 30 cm^{2}

Thus, the total area of margin is 30 cm^{2.}