Объяснение:

6

AB=49

AC=5/2×CB

AC-CB=?

AC=AB-CB

5/2×CB=49-CB

2,5×CB=49-CB

2,5CB+CB=49

3,5CB=49

CB=49:3,5

CB=14

AC=5/2×14=35

AC-CB=35-14=21

7

AB=3x

BM=x

BM=5

5=X=BM

AB=3×5=15

AC=2×(AB+BM)=2(15+5)=2×20=40

8

AC=2(AM+MB)

AM=x

MB=2X

MB=6

6=2X

X=3=AM

AC=2(AM+MB)=2(3+6)=2×9=18