convert regexp word to number

       case bput("get water from my #{@bag}", 'What were', 'You get')
          when 'What were'
            existing = 0
          end
          when 'You get'
             bput('count my water', 'There are \w parts of water left.').scan(/\w/)
                existing = Regexp.last_match(1)
                val_map = { 'one' => 1, 'two' => 2, 'three' => 3, 'four' => 4, 'five' => 5, 'six' => 6, 'seven' => 7, 'eight' => 8, 'nine' => 9, 'ten' => 10, 'eleven' => 11, 'twelve' => 12, 'thirteen' => 13, 'fourteen' => 14, 'fifteen' => 15, 'sixteen' => 16, 'seventeen' => 17, 'eighteen' => 18, 'nineteen' => 19, 'twenty' => 20, 'thirty' => 30, 'fourty' => 40, 'fifty' => 50, 'sixty' => 60, 'seventy' => 70, 'eighty' => 80, 'ninety' => 90 }
                value = value.map { existing| val_map[existing] }.inject(&:+)
                stock_needed = ((quantity * recipe['volume'] - value) / 100.0).ceil
          end

The error on the screen:
workorders: *** No match was found after 15 seconds, dumping info]
[workorders: messages seen length: 3]
[workorders: message: There are eighteen parts left of the water.]
[workorders: message: [DRPrime]-DR:Weeks: "ahh"]
[workorders: message: Sephiram just arrived.]
[workorders: checked against [/There are \w parts of water left./i]]
--- Lich: error: nil can't be coerced into Fixnum