Look at the first 20 letters of the alphabet below.
Starting counting the letters from 'A'.
A is 1
B is 2
C is 3
D is 4 ...
Continue all the way until....
T which should be 20
Find the letter which is 10th in the alphabet.
A1 - B2 - C3 - D4 - E5 - F6 - G7 - H8 - I9 - J10
J is the 10th letter.