Final answer:
Marshall has breached his duty of loyalty to DigitoolArt Corporation by making a secret profit from a kickback, compromising his obligation to act in the corporation's best interest.
Step-by-step explanation:
Marshall has committed the breach of duty of loyalty known as making a secret profit. In this scenario, by accepting a kickback from Bronson, Marshall has violated his duty to act solely in the best interests of DigitoolArt Corporation. The duty of loyalty requires an agent to avoid situations where a conflict of interest might compromise the agent's ability to act in the best interests of the principal (in this case, the corporation).
Rather than seeking the best deal for DigitoolArt Corporation, Marshall allowed his decision to be influenced by a personal financial gain, which stands in direct conflict with his obligations to the corporation.