Answer:
First row. = -393 74 287
Second row = 471. 162 91
Third row =251 222 - 349
Step-by-step explanation:
For the first row
Cofactor of 12= (-8*15)-(21*13)
= -120-273
= -393
Cofactor of 23 = (11*15)-(7*13)
= 165-91
= 74
Cofactor of -6 = (11*21)-(-7*8)
= 231+56
= 287
For the second row
Cofactor of 11 = (23*15)-(21*-6)
= 345+126
= 471
Cofactor of -8 = (12*15)-(7*-6)
= 120 + 42
= 162
Cofactor of 13 (12*21)-(23*7)
= 252-161
= 91
For third row
Cofactor of 7= (23*13)-(-8*-6)
= 299-48
= 251
Cofactor of 21 = (12*13)-(11*-6)
= 156+66
=222
Cofactor of 15 = (12*-8)-(11*23)
= -96 - 253
=- 349
