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

### Instruction:
Mona bikes 30 miles each week to stay fit. This week, she biked on Monday, Wednesday, and Saturday. On Wednesday, she biked 12 miles. On Saturday, she biked twice as far as on Monday. How many miles did she bike on Monday?

### Response:
Mona biked 30 miles this week.
Mona biked 12 miles on Wednesday.
Mona biked twice as far on Saturday as she did on Monday.
Mona biked 30 miles this week.
Mona biked 12 miles on Wednesday.
Mona biked twice as far on Saturday as she did on Monday.
30 = 12 + x + 2x
30 = 3x + 12
30 - 12 = 3x + 12 - 12
18 = 3x
18 / 3 = 3x / 3
6 = x
#### 6

