The expression "Sin 240 Cos 135 Sin 120 Tan 210" can be simplified as follows:

The sine of an angle can range from -1 to 1, so the sine of 240 degrees is:

sin 240 = -0.5

The cosine of an angle can range from -1 to 1, so the cosine of 135 degrees is:

cos 135 = -0.5

The sine of an angle can range from -1 to 1, so the sine of 120 degrees is:

sin 120 = 0.866025

The tangent of an angle is undefined when the angle is equal to 90 degrees plus a multiple of 180 degrees, so the tangent of 210 degrees is undefined.

Therefore, the simplified expression is:

-0.5 * -0.5 * 0.866025 * undefined = undefined.