It is easy to know from the question that the angle AMB is 45 degrees, the angle MAB is 30 degrees, AB=28*0.5= 14, and MB is X. 。

AB/sin(45 degrees) =X/sin(30 degrees)

Solution, X=7 times the root number 2, choose a.

The second question, do vertical bc over a, horizontal d,

Let ab=x, ac=x+ radical number 2+x-2,

BC = xcos(30)+(x+gen Hao 2-2)* cos(45)；

xsin(30)=(x+genhao2-2)*45

Only need to solve x and bring it into BC.