Joel wants to fence off a triangular portion of his yard yard for his chickens. the three pieces of fencing he has to use are 8 feet, 15 feet and 20 feet

The complete question in the attached figure

we know that
in a right triangle
c²=a²+b²
c=20 ft
a=8ft
b=15 ft
so
c²------> 20²----> 400
and
a²+b²-----> 8²+15²------> 64+225-----> 289
so
400 is not 289
therefore

Part A)
the answer is
Joel is not be able to make a right triangle with his fence

Part B)
if Joel cut the longest piece of fencing in order to make a right triangle
then
a²+b²=289
so
c²=√289-------> c=17 ft

the perimeter of the fence is
17+8+15-----> perimeter=40 ft

if Joel takes 30 sec to install----------> 1 ft of fencing
 X--------------------------------------> 40 ft
x=40*30-----> x=1200 sec------> x=1200/60----> x=20 minutes

Part B)
the answer is
 20 minutes