Answer:
4
Step-by-step explanation:
Split 19 into two numbers, 9 and 10. If there are 10 nickels, there are 5 dimes. That means there rest are quarters and there are 4.
edit : im not american and have little knowledge of how much each are worth
x = -6
-18+4y=0 => 4y=18 =>y=18/4=9/2
Y=5
3x+20=0 => x=3x= -20=> x= -20/3