This is a system of equations problem that can be solved using one of three methods: graphing, substitution, or elimination. I'll be using substitution.
In substitution:
1) Solve one equation for either variable. I'll use the first equation because its easier to solve for one of the variables. I'll be solving for y because that will allow us to solve for the value of x faster.
[tex]x+y=60[/tex]
[tex]y=60-x[/tex]
2) Substitute what you get into the other equation:
[tex]20x + 5y = 600[/tex]
[tex]20x + 5(60-x) = 600[/tex]
3) Solve your new equation in step 2 for the variable, x.
[tex]20x + 5(60-x) = 600[/tex]
[tex]20x + 300-5x = 600[/tex]
[tex]15x + 300 = 600[/tex]
[tex]15x = 300[/tex]
[tex]x=20[/tex]
There are D) 20 $20 bills in her drawer.