A Block Moves at 5 M/s in the Positive X

Multiple Choice

A block moves at 5 m/s in the positive x direction and hits an identical block, initially at rest. A small amount of gunpowder had been placed on one of the blocks. The explosion does not harm the blocks but it doubles their total kinetic energy. After the explosion the blocks move along the x axis and the incident block has a speed of:

A) 1.8 m/s
B) 5.0 m/s
C) 6.8 m/s
D) 7.1 m/s
E) 11.8 m/s