Total Contribution per Year for next 10yeras =$1000+$800 =$1800
So Total Future fund Vaule =$1800*(1+1.073+power(1.073,2)+ power(1.073,2)+ power(1.073,3)+ power(1.073,4)+ power(1.073,5)+ power(1.073,6)+ power(1.073,7)+ power(1.073,8)+ power(1.073,9)+ power(1.073,10)) =30938.6145
So The Vaule of Corpus =$30938.6145 =PV
Substituting pv (present value for k and PMT (payment) for a in the equation 12 results in
PV =PMT [1-(1+i)^{-n}]/i
K = The original loan or investment amount.
n = The number of compounding periods constituting the duration of the investment or loan.
K *R^{n} = The future value (FV) of K after n compounding periods (years).
i =The interest rate per compounding period.
a =The annuity
R=(1+i/100)
Expressing the interest rate as a decimal fraction instead of as a percentage value results in
R = (1+ i )
PV =5000*((1-(1+8.7)^{-30})/0.087) =5000*((1-power((1+0.087),-30)/8.7) =52766.21235
So Increase installments = (PV/(1+1.073+power(1.073,2)+ power(1.073,2)+ power(1.073,3)+ power(1.073,4)+ power(1.073,5)+ power(1.073,6)+ power(1.073,7)+ power(1.073,8)+ power(1.073,9)+ power(1.073,10))) =(52766.21235//(1+1.073+power(1.073,2)+ power(1.073,2)+ power(1.073,3)+ power(1.073,4)+ power(1.073,5)+ power(1.073,6)+ power(1.073,7)+ power(1.073,8)+ power(1.073,9)+ power(1.073,10)))
New installment =$3069.923582