Let [t] denote the greatest integer t. Then the equation in x, [x]2 + 2[x + 2] – 7 = 0 has :
no integral solution
infinitely many solutions
exactly two solutions
exactly four integral solutions
C.
If the system of equations
x – 2y + 3z = 9
2x + y + z = b
x – 7y + az = 24,
has infinitely many solutions, then a – b is equal to :