a = still water movement and b = current's effect on movement
Let's start XX using the elimination XXXXXX:
a + b = 126 XXXXX in x XXXXX
a - b = 114 XXXXX in x hours
----------------
2a = 240 XXXXX in x XXXXX
a = 120 miles in x XXXXX
In other words, if XXX water is still, the XXXX XXXXXXX XXX XXXXX in the given time x.
XXX to XXXX XXX current's XXXXXX (b):
XXX + b = XXX
b = X
XXXXX:
120 - X = XXX
XXX = 114
Now XXXX the still water travel distance and XXXXXX XX its XXXXX XX XXXX out how long it XXXXXXXX:
XXX miles / 40 mph = X XXXXX traveled
XX XXX given XXXX is X XXXXX.
X XXXXX affected XX XXX current ÷ X XXXXX = 2 XXX for XXX current