Ответ:

ΔMBN= ΔCBA

MB/CB= BN/BA= MN/CA

6/BC= 4/BA= 5/10

5BC= 4*10

5BC= 60

BC= 60/5

BC=12

CN= BC-BN= 12-4=8

5AB= 4*10

5AB= 40

AB= 40/5

AB=8