i don't know how to solve this question

Application: Mark: 30 For each of the following pairs of vectors, find the following: a. b axb the angle between a & b 1. a = (-6,5,-4) b=(-1,7,-2) 2. a = (-9,-2,1) b=(-10,2,-4) 3. a = (7,2,5) b=(0, 2,-3) 4. a = (-5,10,3) b=(-7,6,2) 5. a = (9,-3,4) b=(3,0,5) 6. a = (-7,-10,-8) b=(0,-8,-7) 7. a = (-2,5,2) b=(5, -2, -1) 8. a = (2,9,4) b=(-4, 2, 7) 9. a = (-1,2,6) b = ( - 5 , 5, 1) 10. a = (-3,-10,-5) b=(-3,9,-10) 11. a = (2,6,1) b=(-4,-3,0) 12. a = (-4,9,-8) b=(4,1,-8) 13. a =(-5,1,-10) b=(0,-2,3) 14. a = (-7,0,-2) b=(10,-6,0) 15. a = (1,2,3) b=(4,5,6)