Implementing a function with 4 inputs with 2x4 decoders
The five 2:4 decoders are simply being used to construct a 4:16 decoder. Each output from this decoder represents one of the 16 possible combinations of input values. This part is going to be the same for any 4-input function.

The only part you need to "design" is which of these 16 outputs you connect to the big NOR gate, and this is simply all of the outputs that correspond to zeros in the K-map for the function. Is this enough of a hint?