A chemical reaction combines two chemicals A and B to make a new compound X. The rate at which the compound X is formed is proportional to the amount of A remaining times the amount of B remaining. The system starts with the two chemicals at quantities A(0)=40 grams and B(0) =50 grams. At time t=0, the chemicals are mixed and X is produced at a rate of 2 grams/minute. Write a differential equation that describes the amount of X as a function of time. Include the necessary initial condition.