1. Write and solve the differential equation that models the following statement, "The rate of change of W with respect to x is proportional to x + 18." 2. In 10 years, the mass of a 200-gram sample of an element is reduced to 100 grams; this is the half-life of the element. Find k for this element. Newtonium (Nt) is a highly radioactive element with a half-life of 625 years. How long would it take 62 grams to decay to 22 grams? (Round your answer to the nearest year.)