Leroy is a citizen scientist for a monarch butterfly project. Every week, he visits a local patch of milkweed and counts the number of monarch larvae on the plants. Last week, Leroy didn't count many larvae. This week, he counts 29 larvae on the milkweed. For both weeks, Leroy's total count is 41 larvae. Which equation can you use to find the number of larvae n Leroy counted last week?