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w=f.x,
so 7=f.2.3
f= 7/2.3 => f= 3.04
energy of a spring is (1/2) k x^2 so k is spring const k= f/ x=> 3.04/2.3 = 1.32
xtra energy will be (1/2)x1.32x (3.9)^2 i.e; 10 j
Answer is 10j
