You didn't include the diagram, but this should be enough to get you started:
If x is in degrees, sin(x) is 0 at multiples of 180.
If x is in radians, sin(x) is 0 at multiples of pi.
If you want the graph to pass through 0 at the named points and x is in degrees, assuming that the sine wave will pass through the X axis after 1/2 of the cycle (i.e., the equivalent of a normal sine wave from 0 to 180 degrees), you'll need to come up with a mapping function that maps x values from -6 to 0, and from 4 to 90. Then you can calculate the sine of the new function. Another way to look at this is that the range from -6 to 4 is 10, and we want to do a conversion to a new range equal to 180. If we call this new function z, then
z = (x + 6)(180/10)
f(x) = sin(z)
Solve for x and simplify. Try substituting some values for x to convince yourself that the function does what you expect.
It is possible to do this for x values in radians rather than degrees, but the mapping function needs to map to the range (0,pi) instead of (0, 180).
