You Have Obtained Data on Test Scores and Student-Teacher Ratios

Essay

You have obtained data on test scores and student-teacher ratios in region A and region B of your state.Region B,on average,has lower student-teacher ratios than region A.You decide to run the following regression.
Yi = β0+ β1X1i + β2X2i + β3X3i+ui
where X1 is the class size in region A,X2 is the difference between the class size between region A and B,and X3 is the class size in region B.Your regression package shows a message indicating that it cannot estimate the above equation.What is the problem here and how can it be fixed? Explain the problem in terms of the rank of the X matrix.