**Given Information:**

- Two computers produced a total of 48000 public utility bills in a day.
- Computer 1 printed bills at a rate of 9600 bills per hour.
- Computer 2 printed bills at a rate of 7800 bills per hour.

**Calculating the Total Time Taken:**

To find out how many bills the second computer had to print after the first computer finished its run, we need to calculate the total time taken by both computers.

Let's assume the first computer took 'x' hours to finish printing all the bills.

- The first computer printed at a rate of 9600 bills per hour.
- So, the number of bills printed by the first computer in 'x' hours = 9600x.

Since the total number of bills is 48000, the number of bills printed by the second computer can be calculated as:

- Number of bills printed by the second computer = Total number of bills - Number of bills printed by the first computer
- Number of bills printed by the second computer = 48000 - (9600x)

**Calculating the Time Taken by the Second Computer:**

The second computer printed at a rate of 7800 bills per hour. So, we can calculate the time taken by the second computer to print the remaining bills as:

- Time taken by the second computer = (Number of bills printed by the second computer) / (Rate of printing of the second computer)
- Time taken by the second computer = (48000 - 9600x) / 7800

**Calculating the Remaining Bills:**

Now, we need to find the number of bills the second computer still had to print after the first computer finished its run. This can be calculated as:

- Remaining bills = Number of bills printed by the second computer - Number of bills printed by the second computer in 'x' hours
- Remaining bills = (48000 - 9600x) - (7800 * x)

Simplifying the equation:

- Remaining bills = 48000 - 9600x - 7800x
- Remaining bills = 48000 - 17400x

**Substituting the Value of x:**

We know that the first computer took 'x' hours to finish printing the bills. To find the value of 'x', we can use the equation:

- Number of bills printed by the first computer = 9600x = 48000

Solving for x:

- x = 48000 / 9600
- x = 5

Substituting the value of x into the equation for remaining bills:

- Remaining bills = 48000 - 17400(5)
- Remaining bills = 48000 - 87000
- Remaining bills = -39000

Since the number of remaining bills cannot be negative, there seems to be an error in the given information or calculations. Please double-check the values provided to ensure accuracy.