You can use the compound growth to work this out,
Firstly you need to make a multiplier for -6%;
1-(6/100) = 0.94
The you times the amount of money by 0.94 to the power of 4 because you are working out 4 years:
230000*0.94^4 = 179527.26
The answer is $179527.26,
Hope this helps! :)