Ok so we are gonna find the area or the rectangles on the object 
Area of rectangle 1 = length x width 
= 6 x 20 
= 120 m square 
Multiply the area of rectangle 1 by 2 because there are two same shaped rectangle.
120 x 2 
=240 m square 
Area of rectangle 2 = 30 x 6 
= 180 m square 
Multiply the area of rectangle 2 by 2 because there are two same shaped rectangle.
180 x 2 
=360 m square 
Area of rectangle 3 = 30 x 20 
= 600 m square 
Multiply the area of rectangle 3 by 2 because there are two same shaped rectangle.
600 x 2 
=1200 m square 
Then add all the area of the rectangles.
240 + 360 + 1200 
= 1800 m square 
Therefore the surface area is 1800 m square