Final answer:
To change a bench's opacity to 80% and the blending mode to color burn, use the Transparency panel found under Object > Effects > Transparency in most graphic design software.
Step-by-step explanation:
To change the bench's opacity to 80% and set the blending mode to color burn in a software application like Adobe Photoshop, you would typically use the Transparency panel. The correct menu option to achieve this would be Object > Effects > Transparency. Here, you can adjust the opacity slider to 80% and from the blending mode dropdown, choose Color Burn to apply that effect.