Circles

Two circles
C1:x^2+y^2+4x-4y-5=0 and
C2:x^2+y^2-8x+4y+7=0 are given
(a)Prove that C1 and C2 touch each other externally
(b)Find the equation of the common tangent to both C1 and C2 which passes through the point of intersection of C1 and C2