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PART C: THINKING 6. Determine if the vectors a = [-1, 5, 3], b = [-2, 4, 7], and c = [10, 7, 1] are coplanar. [4] 7. Given a = [4, 7, 1] and b = [-3,1, 5]: a) Calculate the angle between a and b. [3] b) If c = [3, -4, t], find t so that a and c are perpendicular. [3]