A block of weight \( \mathrm{W} \) produces an extension of \( 9 \m...

A block of weight \( \mathrm{W} \) produces an extension of \( 9 \mathrm{~cm} \) when it is hung by an elastic spring of length
\( \mathrm{P} \) \( 60 \mathrm{~cm} \) and is in equilibrium. The spring is cut into

W 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 the figure. Find the extension in springs.
(1) \( 1 \mathrm{~cm} \)
(2) \( 2 \mathrm{~cm} \)
(3) \( 3 \mathrm{~cm} \)
(4) \( 4 \mathrm{~cm} \)