Denis, the problem was NOT to "solve for b", it was to solve for x, y, and z in terms of b. I would, slightly different from what Denis suggests, let u= 1/40212.4 and v = 1/22619.4. The equations become
bux + y ( (4/3) - bv ) + 2z = (50/3)
Eq. 2 : (4/3)x + y ( (32/3) - (bv) ) + 4z = (6395/24)
Eq. 3 : 2x + 8y + z = 2125/8
From the last equation, z= (2125/8)- 2x- 8y. Putting that into the first equation,
bux+ y(4/3+ bv)+ (2125/4)- 4x- 16y= (bu- 4)x+ (bv- 44/3)y+ 2125/4= 50/3 so (bu- 4)x+ (bv- 44/3)y= 50/3- 2125/4= 200/12- 6374/12= -6174/12= -1029/2. Putting that value of z into the second equation, (4/3)x+ ((32/3)- bv)y+ (2125/2)- 8x- 32y= -(16/3)x- (64/3- bv)y+ 2125/2= 6395/24. -(16/3)x- (64/3- bv)y= 6395/24- 12348/24= -5953/24.
So we have (bu- 4)x+ (bv- 44/3)y= -1092/2 and -(16/3)x- (64/3- bv)y= -5952/24. Solving those for x and y, in terms of b, is more tedious but should be straight forward.