8% and 1.5% are annual interest rates. When calculating, the monthly interest rate should be divided by 12.

The period from April 15 to June 30th is two and a half months, that is, 2.5 months.

So the original formula is =1450× [1+(8%-1.5%) * 2.5/12.

= 1450×[ 1+(8%- 1.5%)×5/24]