Jack and jill are trying to find the slope of a line segment connecting two points, (x1, y1) and (x2, y2). jack uses the formula m = y2 - y1 x2 - x1 . jill mistakenly uses a different formula, but still gets the right answer. which formula could she have used?

The correct question is
Jack and Jill are trying to find the slope of a line segment connecting two points, (x1, y1) and (x2, y2). Jack uses the formula m = (y2 - y1)/( x2 - x1) . Jill mistakenly uses a different formula, but still gets the right answer. Which formula COULD she have used? A) (x2 - x1)/( y2 - y1) B) (y1 - y2)/( x1 - x2) C) (x1 - x2)/( y2 - y1) D) (y2 - y1)/( x1 - x2)

we know that

the correct formula to calculate the slope is
m=(y2-y1)/(x2-x1)
then 
if both numerator and denominator multiply it by -1

m=-(y2-y1)/-(x2-x1)> m=[-y2+y1]/[-x2+x1]
m=[y1-y2]/[x1-x2]

therefore

the answer is the option 
B) (y1 - y2)/( x1 - x2)