ln(2.21)/(12 * ln(1+0.0833r) )
f(x) = g(x)/h(x)
f ' (x) = (g'(x)h(x) - g(x)h'(x)) / (h(x))^2
(0 - ln(2.21)( 12 * (1/(1+0.0833r)) * (0.0833) ) ) / (12 * ln(1+0.0833r))^2
-12/0.0833 * ln(2.21) * (1/(1+0.0833r)) / (144)(ln(1+0.0833r))^2
-1/(12*0.0833) * ln(2.21) * (1/(1+0.0833r)) / (ln(1+0.0833r))^2
-ln(2.21)/(12*0.0833) * (1/(1+0.0833r)) / (ln(1+0.0833r))^2
Note: The bit on the bottom is (ln(1+0.0833r))^2 not ln( (1+0.0833r)^2 ), so it doesn't simplify to 2ln(1+0.0833r).
-ln(2.21) / (0.9996 * (1+0.0833r) * ( ln(1+0.0833r) )^2 )
That should be it. Not sure how to reduce it any further.