How do you do this one?

Almir can seal a driveway in 4 hours. Working together, he and Louis can seal it in 2.3 hours. How long would it take Louis to seal it working alone?

Thanks in advance.

D:3+4D=19

Driveway (D) = Rate * Time

let Louis' time alone be t hours
so Louis' rate is D/t
Almir's rate is D/4
their combined rate is D/2.3

so D/4 + D/t = D/2.3

divide by D,

1/4 + 1/t = 1/2.3

2.3t + 9.2 = 4t

I got t=5.411 hours
So Louis' rate alone is 5.4 Hours

thanks!