Another and I think easier method (w/o using a calculator to solve it for you) is to use Cramers Rule (well, not for 3 unknowns, but its not too difficult). First, you put the variable coefficients into a 3x3 matrice.
31 12 -24
18 24 1
12 -6 4
det of ^ = 11946
Finding this makes things later easier.
then substitue the 4th column into the varible you want to solve for.
105 12 -24
77 24 1
5 -6 4
det of ^ = 21042
Then you take and the "determinent of the variable" matrice and divide the "determinent of the original" matrice. ie. 21042/11946~=1.7614
Do that for y and z.
the answers should be y=1.9345 and z=-1.1326.
This may be the method your child learned in class, but i'm not sure since I wasn't there. Some people on here wouldn't be able to do simple math w/o a calculator
