Note here that longest side is of 40cm for a new haxagon. Hence each of it's side

must be four times that of small hexagon due to similarity. Hence sides of larger hexagon must be 20cm , 24cm , 28cm , 32cm , 36cm and 40cm respectively.

Note another important fact that if two triangles are congruent and sides are in the proportion

x:y , then there area is in proportion x^2 : y^2. Here x:y = 1:4 . Hence x^2 : y^2 = 1:16.

This is because hexagon can be considered to be made of 4 triangles.

Now since smaller hexagon has area 123 sq. cm , the larger hexagon with longest side 40 cm has area equal to 123*16 = 1968 sq. cm.