Yeah the answer is actually C.
I figured it out last night.
Let A(t)=the average salary of all employees on the task force, A(m)= the avg. salary of managers, and A(d)=avg salary of directors. Then from (1), we have that A(m)=A(t)-5000. Insufficient. From (2), we have that A(d)=A(t)+15000. Insufficient.
Together, we have that the A(t)=(A(m)*M+A(d)D)/(M+D) where M and D are the amount of directors. So A(t)*M+A(t)*D=A(m)*M+A(d)*D. Substituting in (1) and (2), we get that A(t)M+A(t)D=A(t)M-5000M+A(t)D+15000D. Cancelling out yields 5000M=15000D. So M=3D. So the directors are 75% of the task force.
ooh... yeah. Its always a good thing to write down the equations. It gives u a better picture.