Let x be the number of couple tickets and let y be the number of single tickets sold.
We know that the school earned a total of $7050, then we have that:
Now, we also know that the total number of students was 173, then we have:
Hence we have the system of equations:
To solve this system we multiply the second equation by -50, then we have:
Adding this equation we have:
Once we know the value of x we plug it in the second equation to get y:
Therefore, they sold 64 couple tickets and 45 single tickets.