If x is the candy Chuck initially has, then after he gave 1/4 of he candy to Ben and 1/6 of the candy to Brenna, he obtains:
x - 1/4 x - 1/6 x
by using the least common multiple you have:
LCM of the denominators = 12
(12 - 3 - 2)/12 x = 7/12 x
Hence, Chuck have left 7/12 of the candy for himself