Answer
m = 10 units
YZ = 60 units
Step-by-step explanation
The question tells us to calculate the length of YZ. From the solution to the other question in the image you shared, it is evident that XZ is a straight line and Y lies in between X and Z.
If XYZ is then a straight line, it is easy to see that
XZ = XY + YZ
XZ = 81
XY = (2m + 1)
YZ = 6m
So, substituting thes values into the expression, we can obtain
XZ = XY + YZ
81 = 2m + 1 + 6m
81 = 8m + 1
We can rewrite this to have
8m + 1 = 81
Subtract 1 from both sides
8m + 1 - 1 = 81 - 1
8m = 80
Divide both sides by 8
(8m/8) = (80/8)
m = 10
But,
YZ = 6m
YZ = 6(10) = 60 units
Hope this Helps!!!