This is somewhat difficult to estimate but assuming your parents were invested in savings bonds, US Treasuries, or basic bank savings/money market funds the average rate for 2008 was approximately 2-2.5%.
using this as a baseline I would estimate the balances that would be required to earn 45K on 2-2.5% growth would be approximately 2,250,000 to 1,800,000.
But if they were invested in other items then this figure would be distorted.
They could have held personal loans or other items which would have generated a larger return (i.e. 7%)
Assuming a maximum rate of 10% then the amount would be about 450,000.
Ok. Thanks. I appreciate that response. I'm just doing some investigating. Thank you again!