Final answer:
A uniformly distributed beam supported by 4 supports typically has 4 reactions; one at each support, assuming there are no horizontal or rotational restraints.
Step-by-step explanation:
For a uniformly distributed beam supported by 4 supports, there are multiple support reactions, each correspond to a vertical force, and depending on the constraints of the supports, possibly horizontal forces and moments. Typically, in the simplest statics model, with each support allowing only vertical movement and no horizontal or rotational restraint, there would be a total of 4 reactions (one at each support).
In reality, if the beam is also able to rotate at the supports, or if any of the supports prevent horizontal translation, the number of reactions can be greater due to the additional forces and moments that need to be considered.