I have a computer program written in BASIC language in the 70's on a cassett tape. Are there computers available today that can read the tape for me?
What kind of computer? For the most part, each kind of computer had its own tape format. Even when two used the same tape interface (e.g., Kansas City Standard), there were still incompatibilities in how BASIC programs were stored.
As long as the computer you used wasn't too obscure, it's likely that a suitable computer can be found. If the tape is in good condition (not sticky, and not too much printthrough), it can probably still be read.