They tell you that the first term is 7 so that cancels out the last answer choice immediately. Then they tell you that each term is multiplied by 4 so when you multiply 7x4 you get 28. This cancels out the second to last answer. Then keep multiplying by 4. 28x4 is 112. 112x4 is 448. Therefore, the obvious answer is the first choice! 7, 28, 112, 448