we know that
[the length of a circumference]=2*pi*r
for r= 4 units
[the length of a circumference]=2*pi*4--------------> 25.12 units
if a full circle (360°) has a length---------------------> 25.12 units
arc for an angle of 72 °---------------------------> X
X=72*25.12/360------------> 5.024 units
the answer is
the length of the subtending arc for an angle of 72° is 5.024 units