Exercise 10.0.13 (C-Level). Check that V2, V3, V4, vs E ker(61) by the definition of kernel. Exercise 10.0.14 (B-Level). Check that Bker(61) forms a basis for ker(61) by first showing these four vectors are linearly independent and then using the Rank-Nullity theorem and an analysis of the pivot(s) of 61 above to conclude it must be a basis for "dimension reasons".