NDA

In NDA written, it's nearly 300 marks out of 900 with at least 25% in each subject. And for SSB, it's 700 out of 1800.

Joining to any Indian Services requires test and exams to clear. They check the abilities of the candidates over through tests. I suggest you to prepare for the NDA exams and attempt it to get into Indian Army. I am sharing with you below link where you can find the eligibility, exams and how to join Indian Army. It can help you to prepare for it. https://www.google.com/url?sa=t&source=web&rct=j&url=http://joinindianarmy.nic.in/alpha/login.htm&ved=2ahUKEwjIj7nx_o3iAhXLqY8KHdIUCXMQiB0wAnoECAgQDA&usg=AOvVaw1svR9ul-YSXVnsqY2KwRPn.

Yes, you can join, but for that you have to apply and clear NDA procedure and after that you will be given choice of opting for, after that you can be able to join Indian Navy or you can also opt for the TES.

Yes, any small step taken to improve yourself of course helps you in the future.
Good Luck!

There is no minimum cutoff in 12th standard for NDA exam. You just have to pass the exam and apply for NDA exam.

There is no minimum number of attempts. Until the age of 19, you can attempt infinitely.

Hi Kartik,
As you have scored well in both the papers, you will be definitely able to clear this written exam. But at the same time, you must know cut off vary every year.
Best of luck.

No, level of Mathematics in agriculture will be of elementary levels that is class 10th level.

Education qualification for NDA exam is that candidate have to qualify class 12th with PCM (Physics, Chemistry, Mathematics). Minimum Height of candidate should be 157 cm for Navy as well as Army. For Air force, Minimum Height required is 163 cm.