Using cramer's Rule to solve for x2, i'm confused on this example

[mr_coffee]

I scanned the page out of the book, alittle bit is kinda burly but I'm confused on how they got A_2(B), where we are thinking of the system in matrix form AX = B. One verfies that detA = -127 and det[A_2(B)] = 313, so
x2 = det[A_2(B)]/det(A) = 313/-127 = -313/127;

How did they get B? and det[A_2(B)] here is the picture:
http://img416.imageshack.us/img416/9428/lastscan5eu.jpg
thanks.

 

[mr_coffee]

nevermind i found the pattern, all they do is replace the 2nd column with the values after the =.

 

[TD]

Correct, to find the 'n-th' unknown with Cramer's rule, you have to replace the n-th column by the column of the constants.