Let 'ℓ'  be the original length and ℓ3  be the length of the wire when the tension is 9N. We know e∝F ⇒ (ℓ1−ℓ)∝4.....(1),(ℓ2−ℓ)∝5.....(2)(ℓ2−ℓ)∝9.......(3)From 'l'(1)&(2)ℓ1−ℓℓ2−ℓ=45⇒5ℓ1−5ℓ=4ℓ2−4ℓℓ=5ℓ1−4ℓ2............(4)From (1)&(3)ℓ1−ℓℓ3−ℓ=49    Put  is above equation and we get ℓ3=5ℓ2−4ℓ1