1. At the start of a reaction, there are x grams of chemical X present. At timer seconds after the start, the rate of decrease of x is proportional to xr. a Using k as constant of proportionality, where k>0, form a differential equation to model this reaction rate. b Solve the differential equation obtaining a relation between x, 1 and k. c Initially, there are 150 grams of chemical X present and after 10 seconds this has decreased to 120 grams. Find the time after the start of the reaction when the amount of chemical X has decreased to 1 g gram.