Level 61
No need to use the supplied marble, this one is about building a bridge. Place two long bars down in the groove, vertically on top of each other. Put the tiny block on top of these as well. Slot another beam vertically in the left-hand section, and then put one across the top of the whole thing. This should be sturdy enough to let the cart cross.
Alternative solution
Luisa also sent in this solution:
