Final answer:
Naomi has 19 coins in total when she has 10 nickels and 9 quarters. For a variable amount of coins, the total is represented by the sum of xx nickels and yy quarters.
Step-by-step explanation:
The question is asking us to calculate the total number of coins Naomi has based on the given numbers of nickels and quarters.
Firstly, if Naomi has 10 nickels and 9 quarters, she simply has 10 + 9 = 19 coins in total.
Secondly, if Naomi has xx nickels and yy quarters, the total number of coins she has can be represented by the equation xx + yy. This is a simple algebraic expression for the sum of two variables, each representing a quantity of coins.