First, solve for tan 0.
Using the unit circle, at the degree of 0, tan(0) = 0/1 = 0.
So, you are now essentially solving for the sine inverse of 0.
When finding the sine inverse of something you look for the angle represented on the unit circle. In this case, at 0 degrees, the y-coordinate that represents sine has a value of 0.
Thus, at 0 degrees, sine is 0.
So, sin^-1(tan(0)) = 0.