Why does math get so hard that you have an answer but you forget what your answer was because it was so so so so so so so so so so so so so so hard. Why is it hard?

Which of the following are arithmetic sequences? check all that apply. a. 0.3, 0.6, 0.9, 1.2, 1.5, b. 2, 3, 6, 11, 18, c. 150, 147, 144, 142, d. 2, 4, 9, 16, 25,