Rate problems

Pedro can paint a fence 50% faster than Juan and 20% faster than Pilar and together they can paint a given fence in 4 hours. How long will it take Pedro to paint the same fence if he had to work alone?

Solution:
Let Rate of pedro = 1/tpedro = x
Rate of juan = .50x
Rate of pilar = .80x
(x+.50x+.80x)4=1
2.3x=1/4
x=5/46
5/46 = 1/tpedro
tpedro=46/5 =9.2hours