A lamb grows with its mass proportional to the cube of its length. When the lambs length changes by 15.8% its mass increases by 17.3kg. Find the final mass.

Really stumped thanks for any help

m_{f}=kx_{f}^{3}

length change by 15.8%

x_{i}+.158x_{i}=x_{f}

x_{f}=1.158x_{i}

m_{f}=k(1.158x)^{3}

m_{f}=1.55kx^{3}

I couldnt get the right answer because at this point, my book shows kx^{3} turning into m_{i} and continuing the problem from there. Why?

kx^{3}=m_{i}

m_{f}=1.55m_{i}

m_{i}=m_{f}/1.55

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