Answer:

Step-by-step explanation:
Given


Required
The explicit formula
First, calculate 
Set n=2; So:


Substitute -25 for 


Calculate the common difference (d)



So, the nth term is:


Open bracket

Collect like terms


11.9 would be the correct answer I believe
Answer:
Uranium-234 is an isotope of uranium. In natural uranium and in uranium ore, U-234 occurs as an indirect decay product of uranium-238, but it makes up only 0.0055% (55 parts per million) of the raw uranium because its half-life of just 245,500 years is only about 1/18,000 as long as that of U-238.
Step-by-step explanation: