The answer is 27 yards squared
17,190 / 5,730 = 3. This means we must divide 70mg in half 3 times
70 / 2 = 35
35 / 2 = 17.5
17.5 / 2 = 8.75
There will be 8.75 mg left after 17,190 years.
I find it best to switch everything exponents when taking derivatives.
F(x) = 7/x
Same as..
F(x) = 7x^-1
Take derivative..
F'(x) = -7x^-2
Plug in x = 1
F'(1) = -7(1)^-2
F'(1) = -7