The total utilities of the first 5 units of good X are 10, 19, 26, 33, and 40 utils, respectively. In other words, the total utility of 1 unit is 10 utils, the total utility of 2 units is 19 utils,...

The total utilities of the first 5 units of good X are 10, 19, 26, 33, and 40 utils, respectively. In other words, the total utility of 1 unit is 10 utils, the total utility of 2 units is 19 utils, and so on. What is the marginal utility of the third unit?