Maths Problem(continuous function)

a
x^2 is continuous
4-x is continuous
x^(1/3) is also continuous, because -(-x)^(1/3) = x^(1/3) and it cna be defined negatively
Combination of continuous function is continuous.
So, the function above is continuous for all real x

b.
x^2 - 4x is continuous by itself.
(x^2 - 4x) is continuous when (x^2 - 4x)>0 and (x^2 - 4x)<0
(x^2 - 4x) is continuous when (x^2 - 4x)=0, because in both sides it is near to 0.
This function is continuous for all real x