I will answer all four of your questions now, but next time try to ask no more than two questions in one posting session. Too many questions in one session means homeworks. Not many of us like to solve too many homeworks. I am one of them.
And, please acknowledge any answer given you, to show us that you understand the answer or not.
cot 40 deg is not in any calculator.
tan 40 deg is, so we use tan 40 deg.
cot 40 deg
= 1/(tan 40 deg)
In 4 decimal places,
It is same as yours.