Awater tower casts a 100- foot shadow. at the same time, an 8- foot street sign casts a shadow of 6 feet. what is the height of a tower?

Set up and solve an equation of ratios.  Comparing shadow lengths, we get 100/6; comparing heights, we get x/8.  Set these two ratios equal to one another and solve the resulting equation for x:

100       x
=       Then 6x=800, and x = 800 feet^2 over 6 feet.  Your answer 
   6        8

must have the unit of measurement "ft."

52 or what they said ☝️