Possible Clues:

• 'Let ___'
• The Beatles' 'Let ___'
• 'What'll --?'
• The Beatles' "Let __"
• ''How tough can __?''
• Beatles "Let ___"
• "Let ___" (Beatles hit)
• "What'll ___?" (bartender's question)
• "How hard can __?"
• ''Let __'' (Beatles tune)