Answer:
2,100 $28 tickets were sold, and 3,900 $40 tickets were sold!
Step-by-step explanation:
So, we need to write two equations in order to solve this:
We will think of 28 dollar tickets as x, 40 dollar tickets as y.
Now lets make those equations:

and

Now, to solve for x and y, lets set a value for x or y. In this case I will set the value of y:
I will do this by taking
, and subtracting x to the other side, to get y alone:

Now lets plug in y to our second equation:

=

Now combining like terms and solving for x we get:

=

=

Now that we know x, lets solve for y by plugging into our first equation!

=

So now we know that our answer is:
2,100 $28 tickets were sold, and 3,900 $40 tickets were sold!
Hope this helps! :3