How do you find area for an irregular polygon

Two sides of a triangle mesure 20cm and 30cm. what is the measure of the third side

What signals you that factoring by grouping is the best method to use when factoring a problem?

Will mark brainliest for correct answer! i have been on this problem for an hour and can't find the answer. i'm begging here! incase you cant read the instructions in the picture because of too much or too little lighting: note: enter your answer and show all the steps that you use to solve this problem in the space provided. write a list of steps that are needed to find the measure of b. provide all steps as clear as possible, !