Answer: Monetary unit assumption
Explanation: The monetary unit of assumption states that every transaction of the business can be expresses in relation to monetary units and these units will be stable over time. The key point in this assumption is that it assumes monetary units to be stable and dependable.
In the given case, Lawton records transactions in dollars and disregards changes in value of dollars over time. Hence, we can conclude that Lawton is following monetary unit assumption.