• How many months will it take until the interest on R900 at 12% will be R135, if simple interest is used?

If you use simple interest at 12% on R900, then you have:

.12 X 900=R108 simple interest for 1 year or 12 months, therefore to get R135, we have:

135/108=1.25 years X 12=15 months to earn R135 @ 12%.