Answer: 
Step-by-step explanation:
We know that the general form of the exponential decay formula is
, where y is final amount remaining after t time, A is the original amount and r is the rate of decay
Now, the ratio of strontium-90 remaining, p , as a function of years, t , since the nuclear accident. 
Hence, the ratio of remaining since the nuclear accident is
That would be a right angle
Subtract 5 from both sides
a/-8 = 4/7 - 5
simplify 4/7 - 5 to 31/-7
a/-8 = 31/-7
multiply both sides by 8
-a = 31/-7 x 8
simplify 31/7 x 8 to 248/7
-a = 248/7
multiply both sides by -1.
The answer is a = 248/7
The words are the explanations of the steps and the dark bolded words are the work shown for each step.
The greatest common factor of 49 and 84 is 7
