Logarithm! Help!

First, let's calculate the ones inside the parenthesis. 

We have $16*5*\frac{1}{10} = 8$

Now, we just have to find $\log_{1/2} (8)$

Using logs and bases, we have $\log_{1/2} (8) = -3$

So -3 is our answer!

Thanks! :)