RI

Explanation:

Look at the first row of letters - (All in Alphbetical Order)

RST
QRS
PQ - R

Look at the Second row of letters - ( All in Alphabetical Order but Skipping 1 Alphabet)

ACE
CEG
EG - I

Answer RI.

Museum of Mathematics

http://www.youtube.com/user/MuseumOfMathematics

Collaborative Mathematics

http://www.youtube.com/user/CollaboMath

Tec Math

http://www.youtube.com/user/tecmath?feature=watch

Dr James Tanton's channel

http://www.youtube.com/user/DrJamesTanton/videos

That

http://www.thatquiz.org/

Soft Schools

http://www.softschools.com/quizzes/math/

14

5*3=15 Ans is 32-15=17

Join the 2 digits to get the results