How do i know when to divide multiply add or subtract in a math word problem

The lines shown below are parallel. if the green line has a slope of -1, what is the slope of the red line?

In which direction does the left side of the graph of this function point? a(x) = 3x - x2 + 4x - 2

Which graph has figures that can undergo a similarity transformation to justify that they are similar? (obviously not the third one)