Portion of marbles given away: 1/2 + 1/3 = 3/6 + 2/6 = 5/6
Therefore, the 6 marbles left over are 1/6 of the marbles she had to start with.
To find the total number of marbles we divide the number of marbles left over by 1/6
6 / (1/6) = 36
Jabu had 36 marbles to start with