How many hands of 5 playing cards (from a standard deck) contain exactly one pair of cards of equal rank? Use a calculator to compute the numerical value of your answer and explain how you calculated...

Discrete Mathematics.

Look at the image attached below. The final answer should 1098240 (according to teacher). Need help solving it.

Extracted text: How many hands of 5 playing cards (from a standard deck) contain exactly one pair of cards of equal rank? Use a calculator to compute the numerical value of your answer and explain how you calculated it.