Answer:
R28077.05
Explanation:
The compound interest formula is:

where
F = future amount
r = annual interest rate
n = number of compounding periods per year
t = number of years
He invests his money for a total of 6 years, but he makes a withdrawal at the end of 4 years, so we can treat this as a 4-year investment followed by a 2-year investment.
The 4-year investment:
He invests R15000 for 4 years at 13% compounded semi-annually.
The future value at the end of the 4 years is:

F = 24824.94
The withdrawal of R3000:
At the end of 4 years, he withdraws R3000.
R24824.94 - R3000 = R21824.94
The 2-year investment:
Now R21824.94 remains earning 13% compounded semi-annually for another 2 years.

F = 28077.05
At the end of 6 years, he has R28077.05