If I had tried again-
I could solve the problem.
I could have solved the problem.
I could solved the problem.
I could have solve the problem.
সঠিক উত্তর:
I could have solved the problem.
ব্যাখ্যা ও নোট:
এটি 3rd Conditional Sentence. If যুক্ত অংশে Past Perfect (had + V3) থাকলে, অপর অংশে Subject + would/could/might have + V3 বসে।