Find the lowest ASCII sum of deleted characters to make strings equal. This is weighted LCS. Alternative view: find the largest ASCII sum of kept characters (the LCS), then answer = total sum - 2 * kept sum.
Trace on , . Common subsequence "ea" has sum . Delete "s" (115) and "t" (116). Total: . DP: = max ASCII sum of common subsequence. When chars match, add ASCII value. Time: , Space: .