I NEED HELP WITH MY MATH HOMEWORK?

Emil and Olive lived on a farm with their father, Gordon. One day, Emil asked his father, "Dad, what happened to the car we used to have?" Olive overheard this, and said, "Yeah, and we used to have a horse too." Gordon replied, "That tomcat and that old bad were no use. I traded them for our new goat." Emil said, "Hey, that sounds like a food crypt-arithmetic problem. Come on Oliver, let's go see if we can solve it." Each letter stands for a different digit, 0 to 9. No two letters stand for the same digit. TOM + NAG = GOAT. Determine which digit each letter represents and SHOW YOUR WORK!!!