If all 21 coins were dimes, she'd have $2.10. But she has 90 more cents than that. Now for each coin that's a quarter, not a dime, she has 15 cents more. 90/15= 6. So there are 6 quarters, and 21-6 = 15 dimes.
Now we do it backwards to see if it's right. 6 quarters is $1.50, 15 dimes is $1.50, add those together and you get $3. So it's right. 6 quarters, 15 dimes.
Step-by-step explanation: to get 7m alone dirst we must subtract 2 from both sides so 2-2 = 0 and -5 - 2= -7 so 7m= 6n-7 and divide both sides by 7 to get m alone so 6n divided by 7 = 6/7n and -7 divided by 7 equals -1 so we're left with m= 6/7n-1
