n = number of nickels casey has
n is simply a placeholder for a number
4*n = number of nickels Megan has
whatever number Casey has, multiply it by 4 to get Megan's number
We add n and 4n to get 5n. We can think of it as 1n+4n = (1+4)n = 5n
Or we can think of it as 1 nickel + 4 nickels = 5 nickels
The final simplified expression is 5n
