Just divide the numerator from the denominator and it will become easier to you
-5 ÷ 6 = -0.83
-3 ÷ 7 = 0.42 
So, -5/6 < -3/7
Negatives is/are always lesser than positives 
Positives is always greater than negatives 
Good luck on your assignment and enjoy your day!
~MeIsKaitlyn