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

### 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:
If Jacob has 18 hours left to finish his homework, Greg has 18-6 = <<18-6=12>>12 hours left to finish his homework.
Patrick has four hours less than twice Greg has left to finish his homework, which is 12*2-4 = <<12*2-4=20>>20 hours left to finish his homework.
Altogether, they have 12+20+18 = <<12+20+18=50>>50 hours left to finish their homework.
#### 50