Math word problem help

Jeff and Kirk can build a 75 ft wall together in 4 hours. Because Jeff has more experience, he could build the wall by himself 3 hours quicker than Kirk. How long would it take Kirk, (to the nearest minute) to build the wall by himself?

I know the answer is 9 hours and 46 minutes but I have no idea how they got it. Can someone help?

Jeff and Kirk can build a wall together in 4 hours
4[(1/J) + (1/K)] = 1

Jeff can build the wall by himself 3 hours quicker than Kirk
J = K - 3

4[(1/(K - 3)) + (1/K)] = 1
4[(K + K - 3) / (K(K - 3))] = 1
(8K - 12) / (K^2 - 3K) = 1
8K - 12 = K^2 - 3K
0 = K^2 - 11K + 12

solve quadratically
(11 ± √73) / 2
K ≈ {1.23, 9.77} hours

ignore the first answer because jeff would build the wall in negative time. doesn't make much sense
K does the job in 9.77 hours

9 hours and .77 * 60 minutes
9 hours and 46.2 minutes
to the nearest minute
9 hours and 46 minutes