Answer
$84=2\cdot2\cdot3\cdot7$
Work Step by Step
Firstly write $84$ in the form of any two numbers as follows.
$84=2\cdot42$
Since $42$ is not a prime number.
Now factorize $42$ in the form of any two numbers as follows.
$84=2\cdot2\cdot21$
Since $21$ is not a prime number.
Now factorize $21$ in the form of any two numbers as follows.
$84=2\cdot2\cdot3\cdot7$
Since now every factor is a prime number. This is the required answer.