Below is an instruction that describes a task. Write a response that appropriately completes the request in French. Please answer in French.

### Instruction:
 Patrick has 4 hours less than twice the amount of time that Greg has left to finish his homework. Greg has six hours less than Jacob left to finish his homework. If Jacob has 18 hours left to finish his homework, calculate the total number of hours they all have left to finish their homework?


### Response:
 Si Jacob a 18 heures pour finir ses devoirs, Greg a 18-6 = <<18-6=12>>12 heures pour finir ses devoirs.
Patrick a quatre heures de moins que le double du temps qu'il reste à Greg pour finir ses devoirs, soit 12*2-4 = <<12*2-4=20>>20 heures pour finir ses devoirs.
Au total, ils ont 12+20+18 = <<12+20+18=50>>50 heures pour finir leurs devoirs.