Answer:
a] 9 coins
b] x + y coins
Explanation:
How many coins does he have if he has 5 nickels and 4 quarters? We will add the number of nickles (5) to the number of quarters (4).
5 nickles + 4 quarters = 9 coins
How many coins does he have if he has x nickels and y quarters? We will do the same thing as above but will use variables. Since x and y are unknown, we won't be able to simplify it further.
x nickles + y quarters = x + y coins