Hello.
C) x=4π/3
The variable x in the cotangent argument has a unit coefficient, so the period is π, just as it is in the parent function cot(x).
Can you graph y = cot(x)? By subtracting the constant π/6 from the argument, that graph is translated to the right by π/6. Just as with cot(x), it is decreasing everywhere.
Have a nice day