How do you solve the system of equations of #6x + 9y = - 18# and #4x - 9y = - 42#?
Substitute into 2,
Set them up as "layered" algebra problems.
We align the variables under each other, and then use algebra to manipulate the expressions to eliminate one unknown and solve for the other, Then we take that solved variable and use it to find the second (or additional) one. Finally, take both solutions and put them in first solved equation again to validate the answer.
Taking the second equation:
Put them both into the first equation to check: