Answer:
Given
Fund Amount P=20000
Payment each month A=1000
Interest rate per month r=6%/12=0.5%
Let B is balloon payment and N is the total number of Payment
so P=A*(1-(1+r)^-(N-1))/r + B/(1+r)^N
20000=1000*(1-(1+0.5%)^(N-1))/0.5% + B/(1+0.5%)^N
By using the trial and error method we find that N=21
So B/(1+0.5%)^21=1012.53
B=1124.39