Question

solve each system by substitution: -x-y-3z=-9, z=-3x-1, x=5y-z+23

Answer 1

well your second equation gives you the value of z
substitute z into the other two equations

now you have two equations to solve
so you would then make y the subject using one of the two equations you have
then substitute y into the other equation
then you will get a value of x
then substitute your value of x into the equation to get y

then substitute x and y into original equations to get z

Answer 2

let me start you off

-x-y-3z=-9 equation 1
z=-3x-1 equation 2
x=5y-z+23 equation 3

sub equation 2 into 1 and 3

-x-y-3(-3x-1)=-9 equation 1
x=5y-(-3x-1)+23 equation 3

now simplify
and follow my instructions from before