[((83.33-84.42)2 + (83.33-84.42)2 + (85.52-84.42)2 + (84.42-84.42)2 + (85.52-84.42)2) / (5-1)]1/2

First calculate what's inside the brackets( ... ).

Then carry out all the multiplications.

Then carry out the division (85.52-84.42)2) / (5-1).

Then do the additions.

Then multiply the answer by 0.5.

 

The order to calculate this is

brackets first ( )

multiplication *

division / 

addition +

substraction - 

 

You must follow the order in every calculation. Read up on it I maybe wrong with the order of addition and subtraction but I think addition comes before subtraction.