First, find the total amount Jenny saved over 8 weeks.

• Amount saved each week = \$3.75
• Number of weeks = 8
• Total savings = 3.75 × 8 = \$30.00

Then, subtract the amount she had left to find the cost of the book.

• Amount left = \$18.45
• Cost of book = Total savings − Amount left
• Cost of book = 30.00 − 18.45 = \$11.55

The book cost \$11.55.
Check: 3.75 × 8 = 30.00, 30.00 − 11.55 = 18.45. ✓
Final Answer: 11.55 dollars