How to get this answer using calculator in radian mode?
Sin Theta =0.4
Theta = 0.4115 radians
The arcsin function is usually right above the sin function on your calculator. You just have to hit the [2nd] button (usually upper left corner and yellow) and then just hit the sin button
If your calculator is in degrees mode, you will have to multiply the angle you get by Pi/180 to convert it to radians.
Hope this helps.