solve the word problem

Question

Jeff and Kirk can build a​ 75-ft retaining wall together in

4 hours. Because Jeff has more​ experience, he could build the wall by himself 1 hour quicker than Kirk. How long would it take Kirk​ (to the nearest​ minute) to build the wall by​ himself?

Answer 1

1/j + 1/k = 1/4

1/(k-1) + 1/k = 1/4

4k + 4k-4 = k^2 - k

k^2 -9k + 4 = 0

k = 9/2 + (1/2)sqr(81 -16)

k = 4.5 + .5sqr65

k = about 4.5 + 4.03

k = about 8.53 hours alone for Kirk

j = about 7.53 hours alone for Jeff

1/7.53 + 1/8.53 = 1/4

34.12 + 30.12 = 7.53(8.53)

64.24 = about 64.23