geometry,math
posted by mellisa .
Find 3 upper case letters that look the same when rotated 180 degrees. Then, what letter's 90, 180, and 270 degree rotations has this outline? This is also the inside lines formed by the rotation of what letter?

O, H, X

thank you but Then, what letter's 90, 180, and 270 degree rotations has this outline? This is also the inside lines formed by the rotation of what letter?
thanks ,Mellisa 
Find 3 upper case letters that look the same when rotated 180 degrees. Then, what letter's 90, 180, and 270 degree rotations has this outline? This is also the inside lines formed by the rotation of what letter?