Puzzles - Missing letters puzzles

Working through the diagram in columns, from top to bottom, letters move through the alphabet in steps of 5 for the left hand column, 7 for the next one, then 9, then 11.

In each diagram, add the numerical values of the top 2 letters together, divide this by 2 and subtract 2 to give the numerical value of the lower letter.

Split the diagram in half, horizontally and vertically, into quarters. Start in the top left cell of each quarter, and move around it in a clockwise spiral towards the centre. Letters are written in alternate segments, moving forward 7 letters at a time for the top left quarter, 6 letters for the top right, 5 letters for the lower right, and 4 letters for the lower left.