20% down payment:

0.20 * 124000 = 24800

amount financed:

124000 - 24800 = 99200

$99,200 is financed for 30 years at 7.5%

let 'L' represent the amount of the loan

let 'p' represent the monthly payment

let 'r' represent the monthly interest rate

let 'm' represent the number of months

convert values to months:

0.075/12 =0.00625

30 years = 30*12 = 360 months

we then use the following formula to calculated fixed monthly payments:

p = L[r(1 + r)^m]/[(1 + r)^m - 1]

p = 99200[0.00625(1+0.00625)^360]/[(1+0.00625)^359 -1]

solving for 'p' we have p=698.47

the monthly payment will be approximately $698.47 per month