This is the information given:
And we are asked to find BF, DB, and AE
Since segment AB is 42 units long and the point E divides it in two equal parts as indicated by the tick marks, then segment AE = 42/2 = 21 units
AE = 21
Notice that D is the circumcenter of the image. That means that is the center of the circle that goes through the three vertices A, B, and C. Then the segments DC, AD, and DB must be equal to the radius of the circle and therefore equal among themselves. That is DC = 29 units = DB
Then: DB = 29
Notice as well that they give us the value of segment FC = 28 units. That segment is equal in length to segment BF (as indicated by the double ticks on them) therefore, the segment BF = 28 units as well
BF = 28 units.