If you are trying to find the slope of a line that is perpendicular to another line, you would need to change the sign and change it to the fraction's reciprocal.
m = 
Change the sign of the slope:

Finally, make the reciprocal of the original slope (switching the numerator and denominator):

Simplify:
3
Final answer:

Answer:
8
Step-by-step explanation:
9/2 would be converted to 450%