what are the steps for the rate.

so if I had ... um, 50%  then when up by um 80% that the rate?

rate is the  amount of something...or distance etc    divided  by TIME.....

how do I find the rate of a Sphere shrinking?  

ok then

so the time like distance 5m the was 5ft now its 12 in the amount of water in it was 90%.

like that 

I have to make a question that has a sphere shrinking and find the rate to my own question. so will this do distance was 5ft now its 12 in the amount of water in it was 90%? 

and what the answer.

4 minutes 

Shrinking from 5 ft to 1 foot in 4 minutes?

WHAT rate do you want to calculate in your made-up equation?  The RATE of change of DIAMETER? The rate of change of VOLUME?   

I am not sure what your 90% statement has to do with your problem......