Question

I=$54, P=$900, t.= 18 months

Answer 1

Wait what are trying to answer here

Answer 2

Interest=Principal x Rate x Time (in years)

Interest=$54
Principal=$900
Convert 18 months to years by dividing by 12 (there are 12 months in a year) so
Time = 18/12=1.5

Plug into formula you get
54=(900)R(1.5)

54=1350R

Divide by 1350

.04=R
Annual Rate is 4%