Please help, i dont understand

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

The means and mean absolute deviations of the individual times of members on two 4x400-meter relay track teams are shown in the table below. means and mean absolute deviations of individual times of members of 4x400-meter relay track teams team a team b mean 59.32 s 59.1 s mean absolute deviation 1.5 s 245 what percent of team b's mean absolute deviation is the difference in the means? 9% 15% 25% 65%

Which expression gives you the distance between the points (5,1)and(9,-6)