First set up the equation:

Then substitute in known values:

and solve for C

Answer:
length = 76 cm
Step-by-step explanation:
The perimeter = (2 × width) + (2 × length)
264 = (2×56) + (2 × length)
264 = 112 + (2 × length)
264 - 112 = 2 × length
152 = 2 × length
152/2 = length
76 = length
length = 76 cm
So we have 22 riders....each carrying 2 saddle bags.....thats (2 * 22) = 44 bags.....each saddle bag has 3 waters....(44 * 3) = 132 total water bottles