a) unique solution
b) infinitely many solutions. One way to see this: pick any value of z. You can solve for x and y by Gaussian elimination.
c) unique solution. Reorder the equations so that x - 7y = 2 is first. Therefore -2x + 14y = -4.
Next equation: 11y= -5 (Add -2 * (x - 7x = 2) to 2x - 3y = -1)
Third equation: 22y = -10 (Add -3 * (x - 7x = 2) to 3x + y = -4)
The second and third equations are redundant. By inspection, the following system has a unique solution:
x - 7y = 2
d) no solutions. subtract (x + 3y + 3z = 3) from (x - y - z = 4) to get -4y - 4z = 1
add -2 * (x + 3y + 3z = 3) to (2x + y + z = 6) to get -5y - 5z = 0. So you have a contradiction.