Find the value of x, if cos (40° + x) = sin 30°.

Calculations:

Given that cos(40° + x) = sin 30°, and knowing that sin 30° = 1/2, we can set up the following equation:

cos(40° + x) = 0.5

The cosine function cos(θ) equals 1/2 at θ = 60° 

Therefore, the solutions for our equation are:

40° + x = 60°

Solving those two equations for x will give us two possible solutions:

x = 60° - 40° = 20°

So, the values of x for which the original equality holds true are 20°

Hence, option 2 is Correct.