You are executing that line 8675040 times and it is taking 84367.53 seconds to do so, which is an average of 0.00972531884579207 seconds per iteration. Is that slow? 12*90*111 = 119880 divisions are done each time, for an average of 8.1125449164098e-08 seconds per division. Is that slow?
The code internally has to do
double(a) ./ (b+1e-10)
which is an extra operation compared to the case where a is already double. Those extra operations take time.
That said, my tests do tend to suggest that doing the double() yourself is faster, by up to a factor of 5. Try
c = double(a) ./ (b+1e-10);
