Lionel's Lawn Care is a company that maintains residential yards. Lionel's cost for his standard package of mowing, edging, and trimming is $15, and he charges $25 for this service. For a total price of $40, Lionel will also trim shrubs, a service that adds an additional $10 to the total cost of the standard package. What is Lionel's marginal cost of adding the shrub-trimming service to the standard package