Calculating speed and mass using conservation of momentum

A $1.0\text{kg}$‍ cart moving right at $5.0{\displaystyle \frac{\text{m}}{\text{s}}}$‍ on a frictionless track collides with a second cart moving right at $2.0{\displaystyle \frac{\text{m}}{\text{s}}}$‍. The $1.0\text{kg}$‍ cart has a final speed of $0.50{\displaystyle \frac{\text{m}}{\text{s}}}$‍ to the right, and the second cart has a final speed of $2.3{\displaystyle \frac{\text{m}}{\text{s}}}$‍ to the right.

$\text{kg}$‍