Albertus invested the following amounts in a unit trust fund for a period of 6 years. The amounts were invested at the beginning of every year. Beginning of year Amount 1 R8 500 2 R11 200 3 R18 300 4 R17 000 5 R22 500 6 R18 000 At the end of year six (6) the value of his interests in the fund was R90 123.  Calculate The internal rate of return on his investment.