Let the total amount that Sarah deposited be $x using the annuity formula: A=P[((1+r)^n-1)/r] A=future value r=rate n=number of years from the information given: A=$500000 r=2.75% n=65-42=23 years p=$x thus plugging our values in the formula we get: 500000=x[((1+0.0275)^(23)-1)/(0.0275)] 500000=31.50x x=15,872.04883 She deposited 15,873.04883 per year The monthly deposit will therefore be: 15873.04883/12=$1322.67