2x + y = 8
-x - 3y = -12
solve the above system of equations using substitution.

Select all the correct answers. what is 221,000,000,000,000,000,000 expressed in scientific notation?

One line passes through (-7,-4) and (5,4) . another line passes through the point (-4,6) and (6,-9)

What is the expression in factored form? 225x^2 - 144 a. 9(5x+4)^2 b. 9(5x-4)^2 c. 9(4x+5)(4x-5) d. 9(5x+4)(5x-4)