Mensa Geometry & Algebra Problem To Obtain Equation of a Common Tangent Line

 

Two circles are tangent to the x-axis and to each other. One is centered at (x,y) = (4, 16) and the other at (44, 25).  What is the equation of the common tangent line (on the opposite side of the x-axis) in slope -intercept form?  I.e. y = mx + b.