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270

Step-by-step explanation:

The figure B is just one 90° rotation away from becoming A, i.e.,

If we rotate B 90° counterclockwise, we get A.

To obtain the same figure after rotating it (counterclockwise or clockwise), the minimum degrees required are 360

So, B becomes A after 90° of rotation, while A becomes A after 360° rotation (in the same direction)

That means,

(angle of rotation is the angle which A turns about in order to line itself with B)

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That makes it 270°

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.