Physics question-does anyone know how to do this with the working

taking the resistivity of platinoid as 3.3 x 10-7 m, find the resistance of 7.0 m of platinoid wire of average diameter 0.14 cm.

Explanation:

The resistance of a piece of wire is given by

where

is the resistivity of the material

L is the length of the wire

A is the cross-sectional area

In this problem, we have

L = 7.0 m

The diameter of the wire is 0.14 cm, so the radius is 0.07 cm, therefore the cross sectional area is

Therefore, the resistance is

two charges are fixed in place on the x-axis as shown. the charge at x = 0 is negative and has magnitude q = 2 μcoulombs (1 μcoulomb = 10-6 coulombs). the charge at x = d, (d = +12 cm), is positive and has magnitude q = 4 μcoulombs. find a point x = xo along the x-axis at which the electric field is zero.

the answer is b i think