The product of -3 and an unknown number, plus 18, equals 21

Which of the angle pairs can be classified as vertical angles? ∠1 and ∠2 ∠2 and ∠4 ∠3 and ∠2 ∠4 and ∠1 ∠3 and ∠1

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.

You use technology ans find a sum of 6.712e-8. write this sum in standard form