Hey!
First change all the fractions so that they have a common denominator: 40
[tex] 3 \frac{39}{40} = 3 \frac{39}{40} [/tex]
[tex] 3 \frac{19 \times 2}{20 \times 2} = 3 \frac{38}{40} [/tex]
[tex] 3 \frac{1 \times 20}{2 \times 20} = 3 \frac{20}{40} [/tex]
Now order them:
[tex] 3 \frac{39}{40} , 3 \frac{19}{20} , 3 \frac{1}{2} [/tex]
Good luck and hope this helps! :)