A particular radioactive isotope has a decay rate of -0.173% where time is measured in years. A scientist started with 1,490 milligrams of this material. Use the Continuous Decay Formula: F=Pert to find how much of the material will exist in 640 years?

none of these

step-by-step explanation:

23 + 34 add up to 57 so just inform the teacher of this really stupid mistake

-3.5 degrees per hour

step-by-step explanation:

find the unit rate:

-12   1/4 degrees           12.25 degrees

= - = -3.5 degrees per hour

      3   1/2 hours               3.5 hours