Solution:

• 16+16=32

• Thus we have 32-input multiplexer.

• If two 16-input multiplexers drive a two-input multiplexer, and all inputs are connected correctly, the output of the two-input multiplexer will be the 32nd input of the 16-input multiplexers.
• The selection inputs of the two 16-input multiplexers determine which input is propagated to the output of the two-input multiplexer. By selecting the 32nd input on both 16-input multiplexers, that value will be passed through the two-input multiplexer to its output.
• Therefore, if all inputs are connected properly and the selection inputs are set accordingly, the output of the two-input multiplexer will be the 32nd input.