Solve the following sql problem:
How many employees whose performance is poor have a salary of over $50,000 per year?

Schema:
SCHEMA:
- Table: location
  - Column: locationID
    - Samples: [1, 2, 3, 4, 5]
  - Column: locationcity
    - Samples: [Atlanta, Boston, Chicago, Miami, New York City]
  - Column: address
    - Samples: [450 Peachtree Rd, 3 Commons Blvd, 500 Loop Highway, 210 Biscayne Blvd, 1650 Washington Blvd]
  - Column: state
    - Samples: [GA, MA, IL, FL, NY]
  - Column: zipcode
    - Samples: [30316, 2190, 60620, 33103, 15648]
  - Column: officephone
    - Samples: [(404)333-5555, (617)123-4444, (312)444-6666, (305)787-9999, (518)256-3100]
- Table: position
  - Column: positionID
    - Samples: [1, 2, 3, 4]
  - Column: positiontitle
    - Samples: [Account Representative, Manager, Trainee, Regional Manager]
  - Column: educationrequired
    - Samples: [4 year degree, 4 year degree, 2 year degree, 6 year degree]
  - Column: minsalary
    - Samples: [US$25,000.00, US$50,000.00, US$18,000.00, US$100,000.00]
  - Column: maxsalary
    - Samples: [US$75,000.00, US$150,000.00, US$25,000.00, US$250,000.00]
- Table: employee
  - Column: ssn
    - Samples: [000-01-0000, 000-02-2222, 109-87-6543, 109-87-6544, 111-12-1111]
  - Column: lastname
    - Samples: [Milgrom, Adams, Wood, Foster, Johnson]
  - Column: firstname
    - Samples: [Patricia, Sandy, Emily, Harold, James]
  - Column: hiredate
    - Samples: [10/1/04, 1/15/01, 3/12/97, 8/14/05, 5/3/96]
  - Column: salary
    - Samples: [US$57,500.00, US$19,500.00, US$69,000.00, US$55,000.00, US$47,500.00]
  - Column: gender
    - Samples: [F, F, F, M, M]
  - Column: performance
    - Samples: [Average, Average, Average, Good, Good]
  - Column: positionID
    - Samples: [2, 3, 2, 1, 1]
  - Column: locationID
    - Samples: [2, 1, 5, 3, 3]

SELECT COUNT(*) FROM employee WHERE performance = 'Poor' AND CAST(REPLACE(SUBSTR(salary, 4), ',', '') AS REAL) > 50000