Help me with this math plz​

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

The following graph shows the consumer price index (cpi) for a fictional country from 1970 to 1980? a.) 1976 - 1978b.) 1972 - 1974c.) 1974 - 1976d.) 1978 - 1980

Combine the information in the problem and the chart using the average balance method to solve the problem.