Solve for the value of f: ½(6 + 4) + 5f = 10

Which of the expressions (on the photo document i inserted) together represent all solutions to the following equation? 8cos(12x)+4=-4 *the answer should be in degrees.* > i would like for someone to explain the process to find the solutions for this.

Im literally having a mental breakdown

What is the point of inflection for the function f(x)=2cos4x on the interval (0, pi/2)