Suppose the half-life of a substance is 250 years. How long does it take until 10% of the substance remains? (Round your answer to the nearest year.)

A) 450 years.

B) 830 years.

C) 876 years.

D) 922 years.

The answer is B. I would appreciate it if you could let me know step by step.

Also, please only give me the solution based on C*A^t or P(t)=POe^(kt) which is half life formula and ln or e.

Other than that I didn't learned it.

Thank you for your help.