Answer:

And that represent the probability that they take longer than 7 minutes to solve the puzzles.
Step-by-step explanation:
The complement rule is a theorem that provides a connection between the probability of an event and the probability of the complement of the event. Lat A the event of interest and A' the complement. The rule is defined by: 
On this case we have that n= 56 represent the employees selected to solve the puzzles.
We know that 23 out of the 56 selected solved the puzzles in less than 7 minutes.
Let's define the events A and A' like this:
A: Employees solved puzzles in less than 7 minutes
By the complement rule then:
A' : Employees solved puzzles in more than 7 minutes
Based on this we are interested to find the probability for A'
We can begin finding P(A), from the definition of probability we know:

For this case if we replace we got:

And using the complemnt rule we got:

And solving for P(A') we got:

And that represent the probability that they take longer than 7 minutes to solve the puzzles.