Answer:
The system is of equations is:

Where g is the amount of general tickets and r is the amount of reserve tickets.
35 general tickets and 25 reserve tickets were sold.
Explanation:
Let general tickets be represented by g and reserved tickets be represented by r.
Each general ticket sells for $10 each and reserved tickets $15 each. Dave collected a total of $725. Thus:

And a total of 60 tickets were sold. Hence:

Our system of equations is:

We can solve by substitution. First, divide both sides of the first equation by 5:

Next, we can subtract a variable (r in this case) from the second equation:

Substitute:

Distribute:

Simplify:

Subtract:

Using the previous equation:

Substitute and evaluate:

So, 35 general tickets and 25 reserve tickets were sold.