Jess, if Char has 3 times as many as Don, then he has one part to her 3 of the 192 marbles, so there are 4 parts.
192/4 = 48
If one part is 48, Don has 48 and Char has 3(48) = 144.
This is after the giveaway, so Don started with 48 + 50 = 98 and Char started with 144 - 50 = 94.