The total number of rooms is given as 260.
If Johnny wrote x + y = 260,
Then that means the single rooms were represented by y while the double rooms were represented by x. We know this because, the next equation shows
60x + 35y = 14000,
That is, x rooms at 60 dollars plus y rooms at 35 dollars equals to a total of 14000 dollars.
Therefore, we can solve Johnny's system of equations as follows;

That means 64 single rooms were rented out, while 196 double rooms were rented out and that resulted in a total sales of $14,000