Simply you forgot that tha area is in foot square... that means you have to multiply by 50 again the result and you obtain 50 x 377.123 = 18,586... just as in your textbook ...
What is the cost of a swimming pool cover. the pool is bounded by and and it costs $2 / foot for the cover. One unit of the x and y axes are 50 feet.
I have tried the following:
Area under the graph
Area of cover is rectangle less area under the graph.
That multiplied by 50, and then by 2
My textbook has $18,856. I am not even in the same ball park.