book Maths Puzzle Numerical Ability

A building that is 150 ft tall casts a shadow of 20 feet long. At the same time a tree casts a shadow of 2 ft. How tall is the tree?

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book Other Question

Is there anyone who can explain what this equation is and how to calculate it?
I just found it on the web and I know nothing about it. But I do think that:
t=time
j=cycle i^-3

PLEASE SOLVE STEP-BY-STEP