Given: abc is similar to xyc. if yc = 4, bc = 6, xy = 5, then ab =

AB = 7.5  
Since the two triangles are similar, the ratio of the lengths of corresponding sides will be constant. So: 
BC/YC = AB/XY 
 We now just need to solve for AB, substitute the known values, and calculate. So:
 BC/YC = AB/XY
 XY*BC/YC = AB
 5*6/4 = AB
 30/4 = AB
 7.5 = AB 
 So the length of AB is 7.5

8 pounds. Because you'll need 4 pounds to make 10 apple pies, 6 pounds to make 15 apple pies, and 8 pounds to make 20 apple pies.