Prove segment de is parallel to segment ab

We can compare the slopes of the two segments. Two segments (and two lines in general) are parallel if they have the same slope. The slope is computed as

In this case, we have

and

Since both segments have the same slope, namely 0, they are parallel.

i believe it is 0.1m because the measurement of 30.4m limits how precise you can be

you can only be as precise as the least precise measurement