How do u do logarithms where there is a log on one side and a number on the other...

Example-
-21.044=log(P/30)

I don't want just an answer to the example, i need to know how to do it please...

convert your log equation into an exponential equation.
-21.044=log(P/30) <------> 10^-21.044 = p/30
almost zero = p/30
p = almost zero