Let the top of the street lamp be A, the bottom be B, the head of a person be C, the feet be D, the head of the shadow be E, BD=6.6m, DE=2.4m, CD= 1.8. This can be regarded as two triangles, so the triangle CDE is similar to the triangle ABE in proportion, ED: EB = CD: AB, and AB=27/4 can be obtained by substituting the data, so the height of the street lamp is 27/4m.