Let l, b and h are respectively the length, breadth and height of the cuboid, then
l = (5 + 5 + 5) cm = 15 cm
when three cubes are joined we get a cuboid
b = 5 cm and h = 5 cm.
Now,
The Surface Area of the resulting cuboid
= 2 (lb + bh + hl) cm2
= 2 (15 x 5 + 5 x 5 + 5 x 15) cm2
= 2 (75 + 25 + 75) cm2
= 2 (175) cm2
= 350 cm2.