The unit rate per pound is
$1.25
( i divided 3.75 into 3 )
ok distribute the 6 by multiplying it by 1q and -5
5=6q-30-19
Now subtract 30-19
5=6q-11
add 11 to both sides
16=6q
divide both sides by 6
q= 16/6
simplify
16/2=8, 6/2=3
q=8/3
The first two rows of coefficients are identical, so by inspection, the determinant is 0.