The sum of a number and it's blank equals zero

What rotation was applied to triangle def to create d’e’f’?

In the diagram, a building cast a 35-ft shadow and a flagpole casts an 8-ft shadow. if the the flagpole is 18 ft tall, how tall is the building? round the the nearest tenth.

Last week , donnell practiced the piano 3 hours longer than marcus . together, marcus and donnell practiced the piano 11 hours . for how many hours did each young man practiced the piano