A block of weight \( W \) produces an extension of \( 9 \mathrm{~cm} \) when it is hung by an el...

A block of weight \( W \) produces an extension of \( 9 \mathrm{~cm} \) when it is hung by an elastic spring of length \( 60 \mathrm{~cm} \) and is in equilibrium. The spring is cut into two parts, one of length \( 40 \mathrm{~cm} \) and the other of length \( 20 \mathrm{~cm} \). The same load \( W \) hangs in equilibrium supported by both parts as shown in Fig. 14(CF).15(b). The extension in \( \mathrm{cm} \) now is
(A) 2
(B) 3
(C) 6
(D) 9