the complete question is
Given that the area of the shaded sector is 3.91 inches squared and the radius is 3 inches, find the measure of ∠ACB
the picture in the attached figure
we know that
area of a sector A =(∅*pi/360°)*r²--------> when ∅ is in degree
so
∅=A*360°/(pi*r²)
r=3 in
A=3.91 in²
so
∅=3.91*360/(pi*3²)-----> ∅=49.78°
the answer is
the measure of the angle ACB is 49.78°