Hello,

Answer key might not be available. It depends on the source for to provide or not.. or they have it or not.

For the question papers which has no answer key, you can solve them by yourself and ask your friend or teacher to check it out for you.

You can search for individual question answer in your browser. You will get some guide from related questions and you will get  idea how  it is solved.

Regret prescribed books and practice them well. Solve examples and end chapter excersice.

Hope it helps!