Lofty - Inline photos are highly preferred for the future - use the camera icon and you can attach a jpeg directly.
For your use, which appears to be indoor, the three plies can share load equally, provided there's a valid way for the load to get into all three equally (some of the LVL manufacturers list connections for multi-ply LVLs that can be used as a guide.) It's possible that your element above adequately distributes the load to the (3) 2x10s (like if it's a truss with a mid-span bearing it was designed for), or a wall that's roughly a thickness match for the 4.5" wide (3) 2x10s.
The rest of youse, you can use subscripts you know? It's a pain on a phone, I'll admit, but it helps readability down the line.
To your actual question, Lofty, it's six of one, half a dozen of the other, you can look at the total load on the (3) 2x10s, or 1/3 the load on one 2x10. [Again, providing the load distributes evenly to all three in a rational fashion], you can try ForteWeb to design dimensional lumber, if you need something to check your work, they don't present results quite the way you're likely to run your calculations, but if it works on your calculation AND theirs, then that's a positive sign, if not, you can work backwards from their allowable moment to determine how they arrived at the allowable stress (Fb') and Fv'. ForteWeb presents element level capacities (Mallowable, Vallowable), not stress limits. But you can eventually figure out what CL they used.
Although technically, I think they figure out a bracing spacing requirement that will make it work rather than straight up calculating a CL, they seem to iterate on this to figure out what the bracing space limit is for the loads given. CL would somewhat typically be 1.0 for an interior girder or beam or joist with subfloor above it.
If you really want, there are some wood design calculations in college level architecture courses, those can be helpful to refresh your knowledge.