-15/4, -3 1/3, 3.3, 3.5: negative numbers are less than positive numbers, and the largest negative is least, so, since -15/4=-3.75 is more negative than -3 1/3=-3.33 (just as -375 is less than -333), -15/4 is least. Of the two positive numbers, 3.3 is less than 3.5 (just as 33 is less than 35).