What are the takeoff and landing speeds of a Learjet 45?
The takeoff and landing speeds of aircraft can usually be found in the performance section of the aircraft light manual. They are not fixed and vary over a wide range depending on various factors like,


temperature,
density altitude
weight etc.


The table below gives the takeoff speeds for Learjet 45, taken from Learjet 45 AFM:



Learjet 45 Takeoff speeds; table from Learjet 45 AFM

Here, $V_{1}$ is the critical engine-failure speed.  Below this speed, the pilot should abort and bring the plane to a stop if an engine fails. If the engine fails after the aircraft has exceeded $V_{1}$, he/she should continue the takeoff using the remaining engines. 

$V_{r}$ is the rotation speed, which is the speed at which the aircraft can begin to rotate its nose into the air and $V_{2}$ is the takeoff climb speed, which must be reached at an altitude high enough to clear a given obstacle. For FAR 25 aircraft, the obstacle clearance height is 35 ft (10.7 m).

You can also see from the table (and conditions listed on the right) the various factors affecting the takeoff speeds like runway condition, flap setting etc.

The minimum control speed landing $V_{MCL}$ is also a function of altitude and temperature and varies between 98 and 105 KIAS depending on the flap setting. 

The landing approach speed $V_{REF}$ is the airspeed used for landing climb gradient and depends on the factors given above. The following table from the same document gives the $V_{REF}$ speeds for various configurations.



Learjet 45 Landing Approach; table from Learjet 45 AFM

*Speed definitions from www.aerospaceweb.org