homework and exercises - Bird on electric wire: theoretical distance between the two bird legs

Hey guys, please someone help me with this exercise :)

For our exercise, assume that the bird’s body resistance (from leg to leg) is 50kΩ. Given is a high voltage power line with a current of 100A where the bird takes a rest. The high voltage power line is made out of aluminium, which has a conductivity of $3.79\times10^7 \,\rm S/m$ and a cross section of $100\rm\, mm^2$. 
Determine the theoretical distance between the two bird legs.

I know, the formula is V = R x I

I = 100 A, right?

R = ?

Please someone explain step by step?

Thanks.