Similar Figures, find scale factor and solve for missing sides

scale factor -  is the ratio between corresponding measurements of an object and a representation of that object

The second triangle listed is 3 times as large. If you use the ratios, 27/9 = 3 and 21/7 = 3. The second triangle listed is larger, so the scale factor is larger than 1.

This time, the second triangle listed is smaller so the scale factor is smaller than 1. You can use the reciprocal of the answer you got from the previous problem or use the ratios. Make sure to put the smaller number on top if you find the ratios: 9/27 and 7/21 both reduce to 1/3.