Answer:
b.$50,000
Step-by-step explanation:
The paid $90,000 and additional $10,000 spent on this equipment is the cost of this equipment, but maybe have been amortized fully in current project already; so we do not need to indicate these amount in the new project.
The company has received an offer of $50,000 for selling this piece of equipment, thus this is an opportunity cost of the project.
And the company should assign this as an initial cost of the project.