Using the idea that similar triangles are proportional, we can solve this problem fairly easily using a proportion. It is always best to try to draw a picture if possible, as it may increase your understanding of the problem! I have attached an image of the situation.
Proportion: The woman's distance from the laser / the woman's height = the lamp post's distance from the laser / the lamp post's height
2.1 / 1.8 = 4.5 / x
8.1 = 2.1x
x = 3.9m
Hope this helps!! :)
