In everyday conversation, Yeshua and Hillel spoke Aramaic, not Greek.
For various reasons beyond the scope of this site, it is obvious to linguists and translators that the original conversation of Mark 12:28 was either in Aramaic or its sister language Hebrew, which was no longer spoken in everyday use. The actual conversation was definitely not in Greek.
The Aramaic and Hebrew word translated "resources" can properly be translated either "might", "mind", "strength" or "resources", i.e., wealth.
Contrary to common belief, very few biblical Greek translators have a thorough knowledge of First-Century Aramaic. Hence, although a translation may properly translate the text from Greek to English, it may not capture the exact meaning of the actual original words.
Christian Bibles usually translate the word as "mind". This gives rise to debates about "What is the difference between 'heart' and 'mind', since the Jewish understanding of 'heart' in biblical terms is 'mind'?"
Various Jewish sources translate Hillel's statement as "heart, soul, strength and resources", which makes more sense.
Most likely, this is the sense in which Yeshua used the word.