



 
Hi Shifali, I think the statement "the binomial expansion of $(mnx)^3$ is $1+9x+$" means that the constant in the binomial expansion is 1 and the coefficient of the x=term is 9. Do you know the binomial theorem? If so apply it to $(m  nx)^{3},$ and set the constant term to 1. What value does this give for $m?$ Now consider the xterm. I hope this helps, 



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