Since its simple interest then we shouldn't me calculating compound interest,
Rate of interest = 6.0
Time period = 6 years
Expecting amount after 6 years = ​$4500
There for , 4500/(1 + (3*6/100))
which is 4500/(1 + 0.18)
It gives us 4500/1.18 = 3813.56
so we have to put $3813.56