  We find a simple exact solution of 6-dimensional braneworld which captures
some essential features of warped flux compactification, including a warped
geometry, compactification, a magnetic flux, and one or two 3-brane(s). In this
setup we analyze how the Hubble expansion rate on each brane changes when the
brane tension changes. It is shown that effective Newton's constant resulting
from this analysis agrees with that inferred by simply integrating extra
dimensions out. Based on the result, a general formula for effective Newton's
constant is conjectured and its application to cosmology with type IIB warped
string compactification is discussed.
