We first create a system of equations that can represent the problem given.
We let x represent the amount of chocolates, in pounds, and y be the amount of mixed nuts, also in pounds. Colin has a total of 10-lb bag of trail mix. We can write an equation representing this as:

Chocolate costs $3.00 per pound while mixed nuts cost $6.00 per pound. Colin's total budget is around $5.40 per pound. This can be represented in equation as:

Hence, we now have the system of equations written as:

Solve the system of equations using methods of elimination, as follows:


Therefore, Colin used 2 pounds of chocolates and 8 pounds of mixed nuts for this 10-lb trail mix.