Two Blocks,joined by a String,have Masses of 6

Multiple Choice

Two blocks,joined by a string,have masses of 6.0 and 9.0 kg.They rest on a frictionless,horizontal surface.A second string,attached only to the 6.0-kg block,has horizontal force = 45 N applied to it.Both blocks accelerate.Find the tension in the string between the blocks.

A) 18 N
B) 27 N
C) 12 N
D) 9.0 N