What is the total surface area of this composite solid ?

Each of the small 12 identical blocks has dimensions 4 by 5 by 7 inches.

Together they form a larger block of:

width w=5 in
length l = 7 in+7 in+7 in = 21 in 
height h = 4 in + 4 in + 4 in + 4 in=16 in

The total area of the block is:

(front face+back face)+("floor" face + "ceiling" face) + 2 side faces
=
16 * 21 + 16*21 + 5*21+ 5*21 + 5*16+5*16  (square inches)
=
336+336+105+105+80+80  (square inches)

= 672+210+160 (square inches)

=1,042 square inches

1,042 square inches