"Why" is the fundamental scientific question, the question regarding cause and effect. "How" already implies that certain things cause others, and sometimes it seems that cause and effect are not that easy to distinguish.

Does science answer why or how?

It is true that science investigates causal chains, like A — >B — >C, but that's not the answer to a “Why?” question. It's the answer to a “How?” question. Science does not answer why.

Is why and how the same?

“How” and “why” are both interrogative words, but they answer different questions. “How” answers questions like “by what method?” “to what degree?” “in what condition?” and many more. Whereas, “why” answers questions like “for what purpose or reason?”