Three blocks of $1.0\ \text{kg}$, $2.0\ \text{kg}$ and $3.0\ \text{kg}$ are tied in a line by light strings on a smooth floor. A $12\ \text{N}$ pull on the $3.0\ \text{kg}$ block, at the front, drags all three. What is the tension in the string between the $2.0\ \text{kg}$ and the $3.0\ \text{kg}$ blocks?