The Associative Laws say that it doesn't matter how we group the numbers (i.e. which we calculate first) ... ... when we add : (a + b) + c = a + (b + c). ... or when we multiply : (a Ã b) Ã c = a Ã (b Ã c).
To complete the PCT in two months (or less) you will need to average approximately 43.6 mi / 70.2 km per day (this was my longest day on trail).
In water, PCBs are essentially broken down by the effect of sunlight (photolysis). In shallow water, in summer sunlight, it takes 17 to 210 days for half of the amount (initially) present to be broken down for molecules with 1 to 4 chlorine atoms. Breakdown by sunlight is slower during winter.