How does one derive to an answer for different is there a simple rule for 7th grade math?

How do you solve a question like this?

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.

Which sums are equal to 1hold 6/8? choose all answers that are correcta.1/8+6/8b.12/8+2/8c.8/8+1/8+1/8+1/8+1/8+1/8+1/8d.8/8+6/8