well, we know a nickel is 5 cents, a dollar is 100 cents, how many times does 5 go into 100? 100 ÷ 5 = 20, twenty times, so there are 20 nickels in 1 dollar.
these rolls each have 40 nickels though, namely 20 + 20 = 1 dollar + 1 dollar, so there are 2 dollars in one of these rolls.
we know there are 2 bucks in a roll of nickels, how many in 25 rolls? 25 * 2 = $50.