I) 25% of the project at company Z have 4 or more employees assigned to each project.
INSUFFICIENT as we don't know the distribution of 1, 2 or 3 employees in the other 75%.


II) 35% of the project at company z have 2 or fewer employee assigned to each project.
INSUFFICIENT as we don't know the distribution of employees.

I & II Combined:
Look at bands of quantities of employees and the corresponding percentage scales below:
[________<=2)________][_______3_______][_____>=4_______]
[_________________75%________________][______25%______]
[________35%_________][_____________65%_______________]

The median is located at 50.5% which is between 35% and 75%.
3 is the only quantity between 35% and 75%.
Therefore the median is 3.
SUFFICIENT.

I think, answer should be C. Because 35% projects have 2 or less than 2 employees and 25% of projects have 4 or more employees. This means remaining 40% has 3 employees(By Combing both statements)