Explain melting and freezing using the kinetic theory of matter​

Which of the following changes to a pipe would increase the conductance by a factor of 12? 1.quadrupling the length and tripling the radius.2.reducing the length by a factor of and doubling the radius.3.tripling the length and reducing the radius by a factor of .4.reducing the length but a factor of and doubling the radius.

Find the magnetic field a distance r from the center of a long wire that has radius a and carries a uniform current per unit area j in the positive z direction.

What’s #16 asking and how do i solve it?