Find all solutions to sin(x) = -13/40 in the interval [12pi, 16pi]. Answers to 2 decimal places!
Multiply out 12pi and 16pi and find their decimal approximations. This is the interval you are aiming for.
Now, ask your calculator what the inverse sin of -13/40 is. Keep adding 2pi to it until you find every value that is in the range you found above.