Need help fully explaining the solution to this problem

Question: How much should you deposit at the end of each month into an IRA that pays 8.5% compounded monthly to have $1 million when you retire in 40 years? How much of the $1 million comes from interest? Future value = pmt x ((1+r)^n-1))/ PMT = FV = ((1+r)^n-1)}/r ) Monthly deposit = $160.19 (1,000,000/(((1.007083-540)-1)/0.007083)] interest amount = $913,498.67 1000000-(160.19*45*12)