Answer:
Let x be the number of dimes and y the number of quarters
x +y = 100
a dime is $0.10 and a quarter is $0.25
0.1x + 0.25y = 21.40 multiply by 100 to remove the decimals
10x + 25y = 2140, From the first equation y = 100 - x and plug it in to the second equation.
10x + 25(100 -x) = 2140
10x + 2500 - 25x =2140
2500 - 15x = 2140
360 = 15x x = 24 and y = 76
There are 24 dimes and 76 quarters