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back to boardHere's the equation Just prepare the equation as described and solve for c=x,   display_sum + k - (entered_sum + x) == (n + 1) * 2; display_sum + k - entered_sum - x = 2 * n + 2; x = -2 * n - 2 + display_sum + k - entered_sum;   if x < 0 then Big Bang!  |  
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