Answer:
R = 13%
Step-by-step explanation:
P = $4000
I = $780
T = 18 months = 18/12 years
[tex]I = \frac{PRT}{100} \\\\780 = \frac{ 4000 \times R \times \frac{18}{12}}{100}\\\\780 = \frac{6000 \times R }{100}\\\\780 = 60R\\\\R = \frac{780}{60} = 13 \%[/tex]
