Final answer:
If PQ and ST are parallel lines, the width of the lake ST can be found by subtracting the length of any segment on the line PQ from the total length of ST.
Step-by-step explanation:
In the given question, if PQ and ST are parallel lines, then the width of the lake ST can be found by subtracting the length of any segment on the line PQ from the total length of ST.
For example, if PQ represents the width of the lake and ST represents the total length, while PS and TQ represent the segments on the lines, then the width of the lake ST would be expressed as:
ST = PS + PQ + TQ.