According to Santa Cruz, The frame weight of a MED size with a Monarch 3.3 shock is, 4.3lbs (1.952kg).
You can likely find the weight of both the Monarch 3.3 and Fox RP23 on the web and do the math to solve for X.
You can likely find the weight of both the Monarch 3.3 and Fox RP23 on the web and do the math to solve for X.