The difference between 2/5 of a number and 8 is 7/5 of that number

25 meters

Step-by-step explanation:

in this case they give us the information about the lake and that length corresponds to the perimeter.

the perimeter of a circle has the following formula:

p = 2 * pi * r

then r equals:

r = p / pi * 2

replacing we have:

r = 157 / (2 * 3.14)

r = 25

which means that the radius of the lake is 25 meters