Answer:
36
Step-by-step explanation:
Let number of m&ms Garry has be g
number of m&ms Larry has be l
Number of m&ms Jerry has be j
Since Gary has TWICE as Larry, we can write:
g = 2l
Also, Jerry has THRICE as Larry, we can write:
j = 3l
Together, they have 108, thus, we can write:
g + l + j = 108
Putting 1st and 2nd equation in 3rd, we can solve for Larry first. Shown below:

Larry has 18. To find Gary's number, we can use the fact g = 2l, so
g = 2 * 18 = 36
Gary has 36 m&ms