I found this problem while helping my nephew with his "O" level mathematics. My solution doesn't match the answer. Can anybody point out the error in my procedure?
A woman buys a house valued at $\$18000$. She pays $30\%$ of its value immediately, $\$6000$ eighteen months later and the remainder after a further eighteen months. Simple interest is charged at $4.5\%$ per annum. Find how much she pays altogether?
My solution$$18000+(12600 \times 0.045 \times 1.5)+(6600 \times 0.045 \times 1.5) = 19296$$ does not match the answer. The answer given is $\$19350$.