Related Clues:

• 15, for any row, column or diagonal of a 3x3 magic square
• Amount of money; add
• 2 + 2 = 4, e.g
• Society returns Greek letter - it's an answer to additional problem
• Ransom specification
• Figure under a line
• The whole lot sent back letters from Greece
• Only half the season: that's the problem
• The whole amount? Sounds to be less than that
• Briefly, with "in"
• "The ___ of All Fears"
• Altogether number
• Sigma signification
• Mathematical problem
• It all adds up