Answer :

F

Explanation :

Starting with the G and moving clockwise, letters advance through the alphabet in steps of 3 letters, then 4, then 5 etc.

Answer :

N

Explanation :

Starting at the top left hand of every diagram, move around the outer circles in an anti-clockwise direction. Letters are written in alphabetic sequence, in steps given by the numerical value of the central letter.

Answer :

S

Explanation :

Starting at the top left of the diagram, and moving in a Z shape, letters advance through the alphabet in steps of 5.

Answer :

G

Explanation :

Starting with the letters in the top row, and following straight lines through the middle circle, subtract the numerical value of the middle letter (G) and write the letter with the corresponding numerical value in the lower circl

Answer :

M

Explanation :

Working in rows, add together the numerical values of the left and right hand letters to give the numerical value of the central letter.