A non-governmental organization needs a program to calculate the amount of financial assistance for needy families. The formula is as follows:

• If the annual household income is between $30,000 and $40,000 and the household has at least three children, the amount is $1,000 per child.
• If the annual household income is between $20,000 and $30,000 and the household has at least two children, the amount is $1,500 per child.
• If the annual household income is less than $20,000, the amount is $2,000 per child. 

Implement a method for this computation. Write a program that asks for the household income and number of children for each applicant, printing the amount returned by your method. Use –1 as a sentinel value for the input.