Is dividing by a number the same as multiplying by the opposite of the number? explain

Can someone me with this problem i don't understand i need

What is the slope of the line that contains the points (-2,1) and (0,-3)

The number of 8th graders who responded to a poll of 6th grade and 8 th graders was one fourtg of the number of 6th graders whi responded if a total of 100 students responddd to the poll how many of the students responded were 6 th graders