The simple interest earned on $500 at 6% for 18 months?

Ok, the formula we'll use is:

I (interest) = P (principle) x R (rate) x T (time in years)

so we know p, r, and t... this is an easy one... no formula rearranging or anything!! :)

I = $500 x 6% x 18/12

I've put 18 over 12 because the time has to be in years therefore, you divide 18 months by 12 months to get it in years which is 1.5 years.

I = $45

You just divide and you will find x