Answer:
One rose bush = $3
One bunch of ornamental grass = $4
Explanation:
We can set up a system of equations to solve for this. Let cost of 1 rose bush be r and cost of 1 ornamental grass be g. Thus we can form 2 equations:

We can multiply the first equation by -2 so that we can eliminate g. Thus, we have:

Thus, 1 rose bush is $3. Now plugging in r = 3 into the first original equation, we can solve for g:

Thus, 1 bunch of ornamental grass is $4.