The length of BD is 186.
In order to find that we first have to note that BC is the same length as CD since C is the midpoint. Therefore, we can set them equal to each other and find the value of x.
6x + 3 = 4x + 33
2x + 3 = 33
2x = 30
x = 15
Now we can find the length of either BC or CD and double it to get the total length.
BC
6x + 3
6(15) + 3
90 + 3
93
And when we double that, we get 186, which is the length of BD.