The derivative is a lineair operator, meaning that constants can be put up front and the derivative of a sum is the sum of the individual derivatives. So for 16/x², you just have:
(16/x²)' = 16*(1/x²)' = 16*(x^(-2))'
When there's a square root over the entire expression, use the chain rule. If it was only over the first term, write it as a power 1/2 and use a property of powers to put the exponents together: (a^b)^c = a^(bc).