6b
We are given the distance formula on the bottom in red which we can use to find the distance of CB. The formula tells us that we first need to substract the x-values of the two points and the y-values of the two points. When we substract the x-values of the two points, we get 4a, as given in the problem, the calculation would be as follows:
3a - (-a) = 3a + a = 4a
Now, we need to find the difference between the y-values in the same way, by substracting y1 from y2. In this case, y2 refers to the y-coordinate of point B while y1 refers to the y-coordinate of point C. The calculation is as follows:
b - (-5b) = b + 5b = 6b
Our final answer is 6b