Answer:
rate of the current = 2 mph
Step-by-step explanation:
d = rt
Let c = rate of the current
Rate going downstream = c + 40
Time going downstream = 126/(40 + c)
Rate going up stream = 40 - c
Time going upstream = 114/(40 - c)
Since the times are equal, then
126/(40 + c) = 114/(40 - c)
126(40 - c) = 114(40 + c)
5040 - 126c = 4560 + 114c
240c = 480
c = 2 mph
You can use y=mx+b or x-1x/y-1y
11/3 in a mixed number is 3⅔
The C(x) equation is a parabola with a squared "x" and a positive leading term coefficient, meaning, is a vertical parabola and it opens upwards
the lowest point, or lowest cost value, it reaches, is the U-turn point, or vertex

so, the lowest cost is at