Need help figuring this out

I think you want the measure of the arc DF 

$\angle{DEF}=\frac12\,\cdot\,\overset{ \frown}{DF} \\~\\ 72^{\circ}=\frac12\,\cdot\,\overset{\frown}{DF} \qquad \text{ Multiply both sides of the equation by 2.} \\~\\ 144^{\circ}=\overset{\frown}{DF}$

I'll think and then edit this.