The negative numbers are always smaller than the positive ones. So we list those first. The number -3 is smaller than -0.9 since it is further to left on the number line. So far we have -3 followed by -0.9. The last value must be 45 as its the only thing left. The sequence from smallest to largest is therefore -3, -0.9, 45. A number line is recommended to see the values being placed from left to right.
