For this case we have that by definition of trigonometric relations that the sine of an angle is equal to the opposite leg to the angle on the hypotenuse. That is to say:
First we find the y-intercept of this graph whic in this case is -3. Then we plot two pints on the graph and caculate the rise over run which is 2/1=2. Finally, we get the equation- y=2x-3.