I'm terrible at math and need help.

This is how my current software calculates my service:

• $0 charge for miles 0-20
• $2.50 per mile for miles 20-999
• $120 minimum
• Example: 15 miles is $120 / 25 miles is $132.50

I'm testing new software and they don't have tiered mileage capabilities. I'm limited to "minimum price" and "price per mile". If the price per mile computed falls below the minimum price entered, the minimum price will be quoted instead.

This is how the new software is working:

• Minimum price: $120
• Price per mile: $2.50
• Since 40 miles would fall below the minimum of $120, the charge would be $120.
• If it's 55 miles, the charge would be $137.50 (since the minimum has been met)

How can I get the pricing correct on the new system to (somewhat) match the pricing on the current system? Thanks in advance.