I think your question is misleading. To find the "sine of a number" you would use a calculator. But from your examples, it seems you want to solve for x, when x is in a trig function.

Simply take the inverse of the trig function.

The inverse functions are symbolized by the inverse sign, e.g., .

Also, if you are not allowed to use a calculator, the you can use a "unit circle" for common angles.