posted by Angel .
A power station is on one side of a river that is 0.5 mile wide, and a factory is 5.00 miles downstream on the other side of the river. It costs $15 per foot to run overland power lines and $23 per foot to run underwater power lines. Estimate the value of x that minimizes the cost.
The question did not define x, which is probably shown in a diagram.
Let us define x as the distance downstream of the power station across the river, to which point the under-river power line connects.
Then the cost function
You need to minimize C(x) with respect to x.
Can you take it from here?
I will try but there is no diagram.
The solution for x does fit one of the answers. So the interpretation should be correct.