Standard Form and Compound Interest - Comparing Simple and Compound Interest Plans

A small business places \(\$18\ 000\) of unused funds into an investment for \(30\text{ months}\).

Investment R pays \(4.5\%\) per annum compounded every \(6\) months. As a promotion, the bank also credits an additional \(\$120\) into the investment account at the start of the \(30\text{ months}\).

Investment S pays \(4.7\%\) per annum simple interest on the original \(\$18\ 000\).

Which investment should the business choose? Justify your answer.