Hello! Here are the numbers from least to greatest:
-9/4, -0.75, -6/10, 5/3, 2.1
This is because -9/4 is equivalent to -2 1/4, which is less than all of the other numbers. -6/10 (-0.6) is greater than -0.75. 5/3 is less than 2, so it is not greater than 2.1.