Grace is creating a mural for her bedroom wall. She would like to copy a picture that is 3 inches by 4 inches. She uses a copy machine to enlarge it by a scale factor of 3. Then she projects it on her wall by a scale factor of 10. What are the dimensions of the mural?

Grace's original picture has dimensions of 3 inches by 4 inches.

First, she enlarges this picture by a scale factor of 3:

- For the width, \(3 \text{ inches} \times 3 = 9 \text{ inches}\)
- For the height, \(4 \text{ inches} \times 3 = 12 \text{ inches}\)

After the enlargement, the dimensions of the image become 9 inches by 12 inches.

Next, she projects this enlarged image on her wall by a scale factor of 10:

- For the width, \(9 \text{ inches} \times 10 = 90 \text{ inches}\)
- For the height, \(12 \text{ inches} \times 10 = 120 \text{ inches}\)

Therefore, the dimensions of the mural are **90 inches by 120 inches**.