You have 22 quarters and dimes. They total value is $4.90. How many dimes do you have?

4 Dimes

Step-by-step explanation:

You can use the equations you have and solve using either method (graphing, substitution, elimination) substitution works fine!  Since with substitution you to isolate at least one variable, you can use the second equation to get either x or y by itself.  Once you have done that, you can substitute its "value" into the other equation and solve.

so

x(.25) + y(.10) = 4.9

x + y = 22

18(.25) + 4(.20) = 4.9

18 + 4 = 22

x= quarters

y= dimes