Answer:
EF is 16.
Step-by-step explanation:
So we know that Point E is somewhere on Line DF. In other words, DE plus EF must equal DF. In an equation, this is:

We are given that DE is 2x, EF is 2x-6, and DF is 3x+5. So, substitute:

Now, solve for x.
On the right, combine like terms:

Subtract 4x from both sides:

Subtract 5 from both sides:

Divide both sides by -1:

Now that we know x is 11, substitute this back into the equation for EF to find EF.

Substitute 11 for x:

Multiply:

Subtract:

And we're done!