Point b, d, and f are mispoints of the sides of triangle ace. ec= 30 and df= 17, find ac. the diagram is not to scale

You should have a theorem that says that a midsegment between two sides is parallel to and half the length of the third side. 

Since DF is a midsegment = 17, then AC will be 17*2 = 34 

The fact that EC = 30 is extra information, given to throw you off (it worked on me for a bit)