Final answer:
The justification for the conclusion that -5x = 35y is Multiplication Property of Equality.
Step-by-step explanation:
The justification for the conclusion that -5x = 35y is C) Multiplication Property of Equality. The Multiplication Property of Equality states that if you multiply both sides of an equation by the same non-zero number, the equality is still true. In this case, we multiplied both sides of the given equation 3x - 8x = 35y by -5, which allows us to simplify the equation to -5x = 35y.