Answer:
Ellen receives a bunch of fan mail. She splits them all into 3 equal stacks to open up with her mom and sister and each stack contains 21 letters.
To find the total number of letters that Ellen has recieved we have to add up all the letters in the 3 piles.
Your equation would be 21*3=n
You would times 21 by 3 because there are 21 letters in each stack.
Where n would represent the number of letter that Ellen has recieved.
To solve for n you would simply go 21*3=63.
Ellen has revieved a total of 63 letters.
Hope this helps ;)