resistance problem

[Physicsisfun2005]

9 copper wires of length L and diameter d are connected in parallel to form a single composite conductor of resistance R. What must be the diameter of a single copper wire of length L if it is to the the same resistance?

obviously since copper is the only thing involved i know the resistivity is the same given the same distance

R=(resistivity)L/(Area)....i believe this formula may help me...not sure

[maverick280857]

For parallel combination, \frac{1}{R_{eq}} = \sum \frac{1}{R_{i}} where R_{i} = \rho \frac{L}{A}. Express A as a function of diameter.