We know that Resistance Formula :

*R* = resistance | Ω |

*ρ* = specific resistance | Ω×m |

*l* = length of the cable | m |

*A* = cross section area | mm^{2} |

We know that resistance is inversely proportional to square of radius of the wire.

So if the radius of cross section is decreased by x then resistance will be increased by x^{2.}

So in the given question initial radius is 9mm and the radius is decreased by 3mm.

Hence the resistance will be increased by 9 times the initial resistance of the single cable.

So the resistance of the new cable will be **R= 9*10= 90 ohm**