plz help fast will give a fan and a medal

A balloon’s circumference decreases at a constant rate. The graph shows the balloon’s circumference over time.

What is the slope of the line that represents the situation?

Enter the slope as a decimal.
http://static.k12.com/calms_media/media/1512000_1512500/1512349/1/e682f410896cc483335c976d46f50fd393bb1abb/MS_IMC-140516-100013.jpg

Question

plz help fast will give a fan and a medal

A balloon’s circumference decreases at a constant rate. The graph shows the balloon’s circumference over time.
 
What is the slope of the line that represents the situation? 
 
Enter the slope as a decimal.
http://static.k12.com/calms_media/media/1512000_1512500/1512349/1/e682f410896cc483335c976d46f50fd393bb1abb/MS_IMC-140516-100013.jpg

anonymous · Answer

4/5

anonymous · Answer

$$m = \frac{ x _{2}-x _{1} }{ y _{2}-y _{1}}$$

anonymous · Answer

= 4/5

anonymous · Answer

@TardisCuber is close. The sign's wrong

anonymous · Answer

it's 5/4 right

anonymous · Answer

but then i have to make slope as a decimal. how do i do that ???

anonymous · Answer

Crud! I reversed the numerator and denominator in that equation... Sorry. It's -4/5

anonymous · Answer

To turn it into a decimal, use either long division or a calculator. Should get -0.8

anonymous · Answer

oh ok thank you so much