import re
test_str = "Q1_1 - How old are you?"
result = re.sub(r"^Q\d+[a-zA-Z0-9]*_[a-zA-Z0-9]+ +- +", "", "Q1_1 - How old are you?")
if result:
print (result)
aW1wb3J0IHJlCnRlc3Rfc3RyID0gIlExXzEgLSBIb3cgb2xkIGFyZSB5b3U/IgpyZXN1bHQgPSByZS5zdWIociJeUVxkK1thLXpBLVowLTldKl9bYS16QS1aMC05XSsgKy0gKyIsICIiLCAiUTFfMSAtIEhvdyBvbGQgYXJlIHlvdT8iKQoKaWYgcmVzdWx0OgogICAgcHJpbnQgKHJlc3VsdCkKCg==