Please Help I Didn't Understand The Lesson

Which values for a and b will create infinitely many solutions for this system of equations? ax-y=8 2x+y=b

Which term best describes the association between variables a and b? no association a negative linear association a positive linear association a nonlinear association a scatterplot with an x axis labeled, variable a from zero to ten in increments of two and the y axis labeled, variable b from zero to one hundred forty in increments of twenty with fifteen points in a positive trend.

What is the point slope form of a line with slope -5 that contains point (2,-1)