Acollection of dimes and nickels is worth 3.30. if there are 42 coins in total how many of each kind of coin are there?

1 nickels =$0.05
1 dime= $0.1
let the number of nickels be x and that of dimes be y.
total number of coins is given by:
x+y=42
hence:
y=42-xi

total amount of cash will be:
0.05x+0.1y=3.30ii
substituting i in ii we get:
0.05x+0.1(42-x)=3.30
0.05x+4.2-0.1x=3.3
-0.05x=-0.9
x=-0.9/(-0.05)
x=18
hence the the number nickels is x=18, the number of dimes will be y=42-x=42-18=24

The correct answer will be d. -4