First of graph these 2 equations.
In the first one, the derivative is 9x2 - 96 and is zero at ±(4/3)√6. The negative value is the max and the positive one is min.
In the second the derivative is 3x2 - 3 and is zero at ±1. -1 is th max and +1 is the min.
Don't forget to do the 2nd derivative test to determine which is max and which is min.