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

### Instruction:
A notebook costs three times as much as a pen. If a pen costs $1.50, how much will Lyle pay for 4 notebooks?

### Response:
A notebook costs $1.50 x 3 = $<<1.5*3=4.50>>4.50.
So Lyle will pay $4.50 x 4 = $<<4*4.5=18>>18 for the 4 notebooks.
#### 18