Given a wire with a cross section of .45cm^2, a length of 3cm, and an internal resistance of 3 ohms, show your 5 steps to solve for the resistivity of the wire

Resistance ∞ (proportional) length 
resistance ∞ 1/ area

therefore, 
(the constant that we take is known as the resistivity)

resistance =  (resistivity*length )/ area
 resistivity = (resistance * area ) / length
                  = (3 * 45) / 3 =    135/3 = 45 Ωm

in short your answer is 45 Ωm