In the diagram, △ABC,△CDE,△EFG and △HGI are congruent isosceles triangles. B,C,E,G and I are collinear. Suppose that AC and BH meet at M and FG and BH meet at N. Given [HGN]=10, then the value of [BMC] is nm for relatively prime m and n. Find m+n.
[ABC] denotes the area of figure ABC.