A worker can build a fence in 8 hours. with help of an assistant, the fence can be built in 5 hours. how long should it take the assistant, working alone, to build the fence?
1/w + 1/a = 1/5
1/8 + 1/a =1/ 5
1/a = 3/40
a = 40/3 hr = 13 1/3 hr
+36916 
