I'm currently studying for the SAT. I'm taking a practice quiz and came across this problem:
Now, using simple logic (and a bit of cheating by trial and error) we can easily determine the answer to be (D) 20 feet. This seems to be the only explanation I can find. See here. There has just always been a true mathematical explanation. I'm sure this one does too. My first thought is to use proportions but I can't seem to get it right.
So, I'm not asking for an answer here, I wanted to know how to properly do this.