Answer:
15. 0
16. Infinate
17. Infinate
18. -3
19. 11/-6
20. 0
Explanation:
Im not explaining for each cause that would take too long, just know you plug in the y and x into the formula y1-y2/x1-x2. So for the first one, you would have -1--1 / 4--2 but when there are two subtractions signs it turns into a plus so -1+1 / 4+2