Let's first define demand, value and marginal benefit.

Demand is the desire and willingness of a consumer to buy a specific good or service.

The price paid for the good or service is its value.

When the buyer consumes the product, he/she derives satisfaction or happiness. This satisfaction gained is called the total benefit. If the consumer intends to consume an extra unit of the product, he/she will get extra satisfaction which is known as a marginal benefit. So, the marginal benefit is additional satisfaction gained as a result of consuming an extra unit of a product.

Example: Suppose a person go to a hotel and decide to drink coffee (demand). The price which the person is willing and able to pay is the value of that coffee. If that person further decides to buy an extra unit of the coffee, then the satisfaction derived from the second cup is the marginal benefit. Therefore, we can conclude that demand, price, value and marginal benefit are all related.